Methods and systems for utilizing waste sources of metal oxides

ABSTRACT

Methods are provided for producing a composition comprising carbonates, wherein the methods comprise utilizing waste sources of metal oxides. An aqueous solution of divalent cations, some or all of which are derived from a waste source of metal oxides, may be contacted with CO2 and subjected to precipitation conditions to provide compositions comprising carbonates. In some embodiments, a combustion ash is the waste source of metal oxides for the aqueous solution containing divalent cations. In some embodiments, a combustion ash is used to provide a source of proton-removing agents, divalent cations, silica, metal oxides, or other desired constituents or a combination thereof.

CROSS-REFERENCE

Pursuant to 35 U.S.C. §119 (e), this application claims the benefit ofU.S. Provisional Patent Application Nos. 61/073,319, filed 17 Jun. 2008and 61/079,790, filed 10 Jul. 2008, which applications are incorporatedherein by reference. This application is also a continuation-in-partapplication of U.S. patent application Ser. No. 12/344,019, filed 24Dec. 2008, which claims the benefit of U.S. Provisional PatentApplication No. 61/101,626, filed Sep. 30, 2008; U.S. Provisional PatentApplication No. 61/073,319, filed Jun. 17, 2008; U.S. Provisional PatentApplication No. 61/017,405, filed Dec. 28, 2007; U.S. Provisional PatentApplication No. 61/057,173, filed May 29, 2008; U.S. Provisional PatentApplication No. 61/082,766, filed Jul. 22, 2008; U.S. Provisional PatentApplication No. 61/088,347, filed Aug. 13, 2008; U.S. Provisional PatentApplication No. 61/088,340, filed Aug. 12, 2008; and U.S. ProvisionalPatent Application No. 61/121,872, filed Dec. 11, 2008; and which is acontinuation-in-part of International Patent Application Nos.PCT/US08/088246, filed Dec. 23, 2008 and PCT/US08/088242, filed Dec. 23,2008, each of which is incorporated herein by reference in its entirety,and to each of which we claim priority under 35 U.S.C. §120.

BACKGROUND

Carbon dioxide (CO2) emissions have been identified as a majorcontributor to the phenomenon of global warming. CO2 is a by-product ofcombustion and it creates operational, economic, and environmentalproblems. It is expected that elevated atmospheric concentrations of CO2and other greenhouse gases will facilitate greater storage of heatwithin the atmosphere leading to enhanced surface temperatures and rapidclimate change. In addition, elevated levels of CO2 in the atmosphereare also expected to further acidify the world's oceans due to thedissolution of CO2 and formation of carbonic acid. The impact of climatechange and ocean acidification will likely be economically expensive andenvironmentally hazardous if not timely handled. Reducing potentialrisks of climate change will require sequestration and avoidance of CO2from various anthropogenic processes.

SUMMARY

Provided is a method comprising contacting an aqueous solution with asource of metal oxides from an industrial process; charging the aqueoussolution with carbon dioxide from a source of carbon dioxide from anindustrial process; and subjecting the aqueous solution to precipitationconditions under atmospheric pressure to produce a carbonate-containingprecipitation material. In some embodiments, the source of metal oxidesand the source of carbon dioxide are from the same industrial process.In some embodiments, contacting the aqueous solution with the source ofmetal oxides occurs prior to charging the aqueous solution with a sourceof carbon dioxide. In some embodiments, contacting the aqueous solutionwith the source of metal oxides occurs at the same time as charging theaqueous solution with a source of carbon dioxide. In some embodiments,contacting the aqueous solution with the source of metal oxides,charging the aqueous solution with a source of carbon dioxide, andsubjecting the aqueous solution to precipitation conditions occurs atthe same time. In some embodiments, the source of metal oxides and thesource of carbon dioxide are sourced from the same waste stream. In someembodiments, the waste stream is flue gas from a coal-fired power plant.In some embodiments, the coal-fired power plant is a brown coal-firedpower plant. In some embodiments, the waste stream is kiln exhaust froma cement plant. In some embodiments, the source of metal oxides is flyash. In some embodiments, the source of metal oxides is cement kilndust. In some embodiments, the waste stream further comprises SOx, NOx,mercury, or any combination thereof. In some embodiments, the source ofmetal oxides further provides divalent cations for producing theprecipitation material. In some embodiments, the source of metal oxidesand the aqueous solution both comprise divalent cations for producingthe precipitation material. In some embodiments, the source of metaloxides is fly ash or cement kiln dust. In some embodiments, the aqueoussolution comprises brine, seawater, or freshwater. In some embodiments,the divalent cations comprises Ca²⁺, Mg²⁺, or a combination thereof. Insome embodiments, the source of metal oxides provides proton-removingagents for producing the precipitation material. In some embodiments,the source of metal oxides provides proton-removing agents uponhydration of CaO, MgO, or a combination thereof in the aqueous solution.In some embodiments, the source of metal oxides further provides silica.In some embodiments, the source of metal oxides further providesalumina. In some embodiments, the source of metal oxides furtherprovides ferric oxide. In some embodiments, red or brown mud frombauxite processing also provides proton-removing agents. In someembodiments, electrochemical methods effecting proton removal alsoprovide for producing precipitation material.

In some embodiments, the method further comprises separating theprecipitation material from the aqueous solution from which theprecipitation material was produced. In some embodiments, theprecipitation material comprises CaCO3. In some embodiments, CaCO3comprises calcite, aragonite, vaterite, or a combination thereof. Insome embodiments, the precipitation material further comprises MgCO3. Insome embodiments, the CaCO3 comprises aragonite and the MgCO3 comprisesnesquehonite. In some embodiments, the method further comprisesprocessing the precipitation material to form a building material. Insome embodiments, the building material is a hydraulic cement. In someembodiments, the building material is a pozzolanic cement. In someembodiments, the building material is aggregate.

Also provided is a method comprising contacting an aqueous solution witha waste stream comprising carbon dioxide and a source comprising metaloxides and subjecting the aqueous solution to precipitation conditionsto produce a carbonate-containing precipitation material. In someembodiments, the waste stream is flue gas from a coal-fired power plant.In some embodiments, the coal-fired power plant is a brown coal-firedpower plant. In some embodiments, the source of metal oxides is fly ash.In some embodiments, the waste stream is kiln exhaust from a cementplant. In some embodiments, the source of metal oxides is cement kilndust. In some embodiments, the waste stream further comprises SOx, NOx,mercury, or any combination thereof. In some embodiments, divalentcations for producing the precipitation material are provided by thesource of metal oxides, the aqueous solution, or a combination thereof.In some embodiments, the aqueous solution comprises brine, seawater, orfreshwater. In some embodiments, the divalent cations comprise Ca²⁺,Mg²⁺, or a combination thereof. In some embodiments, the source of metaloxides further provides proton-removing agents for producing theprecipitation material. In some embodiments, the source of metal oxidesprovides proton-removing agents upon hydration of CaO, MgO, orcombinations thereof in the aqueous solution. In some embodiments, thesource of metal oxides further provides silica. In some embodiments, thesource of metal oxides further provides alumina. In some embodiments,the source of metal oxides further provides ferric oxide. In someembodiments, red or brown mud from bauxite processing also providesproton-removing agents. In some embodiments, electrochemical methodseffecting proton removal also provide for producing precipitationmaterial. In some embodiments, the precipitation material comprisesCaCO3. In some embodiments, CaCO3 comprises calcite, aragonite,vaterite, or a combination thereof. In some embodiments, the methodfurther comprises separating the precipitation material from the aqueoussolution from which the precipitation material was produced. In someembodiments, the method further comprises processing the precipitationmaterial to form a building material. In some embodiments, the buildingmaterial is a hydraulic cement. In some embodiments, the buildingmaterial is a pozzolanic cement. In some embodiments, the buildingmaterial is aggregate.

Also provided is a siliceous composition comprising a synthetic calciumcarbonate, wherein the calcium carbonate is present in at least twoforms selected from calcite, aragonite, and vaterite. In someembodiments, the at least two forms of calcium carbonate are calcite andaragonite. In some embodiments, calcite and aragonite are present in aratio of 20:1. In some embodiments, calcium carbonate and silica arepresent in a ratio of at least 1:2, carbonate to silica. In someembodiments, 75% of the silica is amorphous silica less than 45 micronsin particle size. In some embodiments, silica particles are wholly orpartially encapsulated by the synthetic calcium carbonate or syntheticmagnesium carbonate.

Also provided is a siliceous composition comprising synthetic calciumcarbonate and synthetic magnesium carbonate, wherein the calciumcarbonate is present in at least a form selected from calcite,aragonite, and vaterite, and wherein magnesium carbonate is present inat least a form selected from nesquehonite, magnesite, andhydromagnesite. In some embodiments, the calcium carbonate is present asaragonite and the magnesium carbonate is present as nesquehonite. Insome embodiments, silica is 20% or less of the siliceous composition. Insome embodiments, silica is 10% or less of the siliceous composition. Insome embodiments, silica particles are wholly or partially encapsulatedby the synthetic calcium carbonate or synthetic magnesium carbonate.

Also provided is a system comprising a slaker adapted to slake a wastesource of metal oxides, a precipitation reactor; and a liquid-solidseparator, wherein the precipitation reactor is operably connected toboth the slaker and the liquid-solid separator, and further wherein thesystem is configured to produce carbonate-containing precipitationmaterial in excess of 1 ton per day. In some embodiments, the system isconfigured to produce carbonate-containing precipitation material inexcess of 10 tons per day. In some embodiments, the system is configuredto produce carbonate-containing precipitation material in excess of 100ton per day. In some embodiments, the system is configured to producecarbonate-containing precipitation material in excess of 1000 tons perday. In some embodiments, the system is configured to producecarbonate-containing precipitation material in excess of 10,000 tons perday. In some embodiments, the slaker is selected from a slurry detentionslaker, a paste slaker, and a ball mill slaker. In some embodiments, thesystem further comprises a source of carbon dioxide. In someembodiments, the source of carbon dioxide is from a coal-fired powerplant or cement plant. In some embodiments, the system further comprisesa source of proton-removing agents. In some embodiments, the systemfurther comprises a source of divalent cations. In some embodiments, thesystem further comprising a building-materials production unitconfigured to produce a building material from solid product of theliquid-solid separator.

DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 provides a schematic overview of an example power plant flue gastreatment process that uses ESP and FGD.

FIG. 2 provides a schematic overview of an example power plant flue gastreatment process utilizing embodiments of the invention.

FIG. 3 provides SEM images of the precipitation material of Example 2 at1000, 2500×, and 6000× magnification.

FIG. 4 provides an XRD for the precipitation material of Example 2.

FIG. 5 provides a TGA for the precipitation material of Example 2.

FIG. 6 provides an SEM image of the precipitation material of Example 3at 2,500× magnification.

FIG. 7 provides an XRD of the precipitation material of Example 3.

FIG. 8 provides a TGA of the precipitation material of Example 3.

FIG. 9 provides an SEM image of oven-dried precipitation material ofExample 4 at 2,500× magnification.

FIG. 10 provides an FT-IR of the oven-dried precipitation material ofExample 4.

DESCRIPTION

Before the invention is described in greater detail, it is to beunderstood that this invention is not limited to particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the invention will be limited only by the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the invention, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Certain ranges are presented herein with numerical values being precededby the term “about.” The term “about” is used herein to provide literalsupport for the exact number that it precedes, as well as a number thatis near to or approximately the number that the term precedes. Indetermining whether a number is near to or approximately a specificallyrecited number, the near or approximating unrequited number may be anumber, which, in the context in which it is presented, provides thesubstantial equivalent of the specifically recited number.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the invention, representativeillustrative methods and materials are now described.

All publications, patents, and patent applications cited in thisspecification are incorporated herein by reference to the same extent asif each individual publication, patent, or patent application werespecifically and individually indicated to be incorporated by reference.Furthermore, each cited publication, patent, or patent application isincorporated herein by reference to disclose and describe the subjectmatter in connection with which the publications are cited. The citationof any publication is for its disclosure prior to the filing date andshould not be construed as an admission that the invention describedherein is not entitled to antedate such publication by virtue of priorinvention. Further, the dates of publication provided may be differentfrom the actual publication dates, which may need to be independentlyconfirmed.

It is noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural references unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the invention.Any recited method can be carried out in the order of events recited orin any other order, which is logically possible.

Materials

As described in further detail below, the invention utilizes a source ofCO2, a source of proton-removing agents (and/or methods of effectingproton removal), and a source of divalent cations. Waste sources ofmetal oxides (e.g., combustion ash such as fly ash, bottom ash, boilerslag; cement kiln dust; and slag such as iron slag and phosphorous slag)may provide, in whole or in part, the source of proton-removing agentsand/or the source of divalent cations. As such, waste sources of metaloxides such as combustion ash (e.g., fly ash, bottom ash, boiler slag),cement kiln dust, and slag (e.g. iron slag, phosphorous slag) may be thesole source of divalent metal cations and proton-removing agents forpreparation of the compositions described herein. Waste sources such asash, cement kiln dust, slag (e.g. iron slag, phosphorous slag) may alsobe used in combination with supplemental sources of divalent cations orproton-removing agents. Carbon dioxide sources, supplemental divalentcation sources, and supplemental proton-removing sources (and methods ofeffecting proton removal) will first be described to give context towaste sources of metal oxides as sources of divalent cations andproton-removing agents. Waste sources of metal oxides will then bedescribed, for example, combustion ash, cement kiln dust, and slag (e.g.iron slag, phosphorous slag) followed by methods in which these wastesources of metal oxides are used to produce compositions comprisingcarbonates.

Carbon Dioxide

Methods of the invention include contacting a volume of an aqueoussolution of divalent cations with a source of CO2, then subjecting theresultant solution to precipitation conditions. There may be sufficientcarbon dioxide in the divalent cation-containing solution to precipitatesignificant amounts of carbonate-containing precipitation material(e.g., from seawater); however, additional carbon dioxide is generallyused. The source of CO2 may be any convenient CO2 source. The CO2 sourcemay be a gas, a liquid, a solid (e.g., dry ice), a supercritical fluid,or CO2 dissolved in a liquid. In some embodiments, the CO2 source is agaseous CO2 source. The gaseous stream may be substantially pure CO2 orcomprise multiple components that include CO2 and one or more additionalgases and/or other substances such as ash and other particulates. Insome embodiments, the gaseous CO2 source is a waste feed (i.e., aby-product of an active process of the industrial plant) such as exhaustfrom an industrial plant. The nature of the industrial plant may vary,the industrial plants of interest including, but not limited to, powerplants, chemical processing plants, mechanical processing plants,refineries, cement plants, steel plants, and other industrial plantsthat produce CO2 as a by-product of fuel combustion or anotherprocessing step (such as calcination by a cement plant).

Waste gas streams comprising CO2 include both reducing (e.g., syngas,shifted syngas, natural gas, hydrogen and the like) and oxidizingcondition streams (e.g., flue gases from combustion). Particular wastegas streams that may be convenient for the invention includeoxygen-containing combustion industrial plant flue gas (e.g., from coalor another carbon-based fuel with little or no pretreatment of the fluegas), turbo charged boiler product gas, coal gasification product gas,shifted coal gasification product gas, anaerobic digester product gas,wellhead natural gas stream, reformed natural gas or methane hydrates,and the like. Combustion gas from any convenient source may be used inmethods and systems of the invention. In some embodiments, combustiongases in post-combustion effluent stacks of industrial plants such aspower plants, cement plants, and coal processing plants is used.

Thus, the waste streams may be produced from a variety of differenttypes of industrial plants. Suitable waste streams for the inventioninclude waste streams produced by industrial plants that combust fossilfuels (e.g., coal, oil, natural gas) and anthropogenic fuel products ofnaturally occurring organic fuel deposits (e.g., tar sands, heavy oil,oil shale, etc.). In some embodiments, waste streams suitable forsystems and methods of the invention are sourced from a coal-fired powerplant, such as a pulverized coal power plant, a supercritical coal powerplant, a mass burn coal power plant, a fluidized bed coal power plant;in some embodiments the waste stream is sourced from gas or oil-firedboiler and steam turbine power plants, gas or oil-fired boiler simplecycle gas turbine power plants, or gas or oil-fired boiler combinedcycle gas turbine power plants. In some embodiments, waste streamsproduced by power plants that combust syngas (i.e., gas that is producedby the gasification of organic matter, for example, coal, biomass, etc.)are used. In some embodiments, waste streams from integratedgasification combined cycle (IGCC) plants are used. In some embodiments,waste streams produced by Heat Recovery Steam Generator (HRSG) plantsare used to produce aggregate in accordance with systems and methods ofthe invention.

Waste streams produced by cement plants are also suitable for systemsand methods of the invention. Cement plant waste streams include wastestreams from both wet process and dry process plants, which plants mayemploy shaft kilns or rotary kilns, and may include pre-calciners. Theseindustrial plants may each burn a single fuel, or may burn two or morefuels sequentially or simultaneously.

Industrial waste gas streams may contain carbon dioxide as the primarynon-air derived component, or may, especially in the case of coal-firedpower plants, contain additional components such as nitrogen oxides(NOx), sulfur oxides (SOx), and one or more additional gases. Additionalgases and other components may include CO, mercury and other heavymetals, and dust particles (e.g., from calcining and combustionprocesses). Additional components in the gas stream may also includehalides such as hydrogen chloride and hydrogen fluoride; particulatematter such as fly ash, dusts, and metals including arsenic, beryllium,boron, cadmium, chromium, chromium VI, cobalt, lead, manganese, mercury,molybdenum, selenium, strontium, thallium, and vanadium; and organicssuch as hydrocarbons, dioxins, and PAH compounds. Suitable gaseous wastestreams that may be treated have, in some embodiments, CO2 present inamounts of 200 ppm to 1,000,000 ppm, such as 200,000 ppm to 1000 ppm,including 200,000 ppm to 2000 ppm, for example 180,000 ppm to 2000 ppm,or 180,000 ppm to 5000 ppm, also including 180,000 ppm to 10,000 ppm.The waste streams, particularly various waste streams of combustion gas,may include one or more additional components, for example, water, NOx(mononitrogen oxides: NO and NO2), SOx (monosulfur oxides: SO, SO2 andSO3), VOC (volatile organic compounds), heavy metals such as mercury,and particulate matter (particles of solid or liquid suspended in agas). Flue gas temperature may also vary. In some embodiments, thetemperature of the flue gas is from 0° C. to 2000° C., such as from 60°C. to 700° C., and including 100° C. to 400° C.

In various embodiments, one or more additional components areprecipitated in precipitation material formed by contacting the wastegas stream comprising these additional components with an aqueoussolution comprising divalent cations (e.g., alkaline earth metal ionssuch as Ca²⁺ and Mg²⁺). Sulfates and/or sulfites of calcium andmagnesium may be precipitated in precipitation material (furthercomprising calcium and/or magnesium carbonates) produced from waste gasstreams comprising SOx (e.g., SO₂). Magnesium and calcium may react toform CaSO4, MgSO4, as well as other calcium- and magnesium-containingcompounds (e.g., sulfites), effectively removing sulfur from the fluegas stream without a desulfurization step such as flue gasdesulfurization (“FGD”). In addition, CaCO3, MgCO3, and relatedcompounds may be formed without additional release of CO2. In instanceswhere the aqueous solution of divalent cations contains high levels ofsulfur compounds (e.g., sulfate), the aqueous solution may be enrichedwith calcium and magnesium so that calcium and magnesium are availableto form carbonate compounds after, or in addition to, formation ofCaSO4, MgSO4, and related compounds. In some embodiments, adesulfurization step may be staged to coincide with precipitation ofcarbonate-containing precipitation material, or the desulfurization stepmay be staged to occur before precipitation. In some embodiments,multiple reaction products (e.g., carbonate-containing precipitationmaterial, CaSO4, etc.) are collected at different stages, while in otherembodiments a single reaction product (e.g., precipitation materialcomprising carbonates, sulfates, etc.) is collected. In step with theseembodiments, other components, such as heavy metals (e.g., mercury,mercury salts, mercury-containing compounds), may be trapped in thecarbonate-containing precipitation material or may precipitateseparately.

A portion of the gaseous waste stream (i.e., not the entire gaseouswaste stream) from an industrial plant may be used to produceprecipitation material. In these embodiments, the portion of the gaseouswaste stream that is employed in precipitation of precipitation materialmay be 75% or less, such as 60% or less, and including 50% and less ofthe gaseous waste stream. In yet other embodiments, substantially (e.g.,80% or more) the entire gaseous waste stream produced by the industrialplant is employed in precipitation of precipitation material. In theseembodiments, 80% or more, such as 90% or more, including 95% or more, upto 100% of the gaseous waste stream (e.g., flue gas) generated by thesource may be employed for precipitation of precipitation material.

Although industrial waste gas offers a relatively concentrated source ofcombustion gases, methods and systems of the invention are alsoapplicable to removing combustion gas components from less concentratedsources (e.g., atmospheric air), which contains a much lowerconcentration of pollutants than, for example, flue gas. Thus, in someembodiments, methods and systems encompass decreasing the concentrationof pollutants in atmospheric air by producing a stable precipitationmaterial. In these cases, the concentration of pollutants, e.g., CO2, ina portion of atmospheric air may be decreased by 10% or more, 20% ormore, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more,80% or more, 90% or more, 95% or more, 99% or more, 99.9% or more, or99.99%. Such decreases in atmospheric pollutants may be accomplishedwith yields as described herein, or with higher or lower yields, and maybe accomplished in one precipitation step or in a series ofprecipitation steps.

Divalent Cations

As disclosed above, waste sources of metal oxides such as combustion ash(e.g., fly ash, bottom ash, boiler slag), cement kiln dust, and slag(e.g. iron slag, phosphorous slag), each of which is described in moredetail in a respective section below, may be the sole source of divalentmetal cations for preparation of the compositions described herein;however, waste sources such as ash, cement kiln dust, slag (e.g. ironslag, phosphorous slag) may also be used in combination withsupplemental sources of divalent cations as described in this section.

Methods of the invention include contacting a volume of an aqueoussolution of divalent cations with a source of CO2 and subjecting theresultant solution to precipitation conditions. In addition to wastesources of divalent cations, divalent cations may come from any of anumber of different divalent cation sources depending upon availabilityat a particular location. Such sources include industrial wastes,seawater, brines, hard waters, minerals, and any other suitable source.

In some locations, industrial waste streams from various industrialprocesses provide for convenient sources of divalent cations (as well asin some cases other materials useful in the process, e.g., metalhydroxide). Such waste streams include, but are not limited to, miningwastes; fossil fuel burning ash (e.g., fly ash, as described in furtherdetail herein); slag (e.g. iron slag, phosphorous slag); cement kilnwaste (described in further detail herein); oil refinery/petrochemicalrefinery waste (e.g. oil field and methane seam brines); coal seamwastes (e.g. gas production brines and coal seam brine); paperprocessing waste; water softening waste brine (e.g., ion exchangeeffluent); silicon processing wastes; agricultural waste; metalfinishing waste; high pH textile waste; and caustic sludge.

In some locations, a convenient source of divalent cations for use insystems and methods of the invention is water (e.g., an aqueous solutioncomprising divalent cations such as seawater or surface brine), whichmay vary depending upon the particular location at which the inventionis practiced. Suitable aqueous solutions of divalent cations that may beused include solutions comprising one or more divalent cations, e.g.,alkaline earth metal cations such as Ca²⁺ and Mg²⁺. In some embodiments,the aqueous source of divalent cations comprises alkaline earth metalcations. In some embodiments, the alkaline earth metal cations includecalcium, magnesium, or a mixture thereof. In some embodiments, theaqueous solution of divalent cations comprises calcium in amountsranging from 50 to 50,000 ppm, 50 to 40,000 ppm, 50 to 20,000 ppm, 100to 10,000 ppm, 200 to 5000 ppm, or 400 to 1000 ppm. In some embodiments,the aqueous solution of divalent cations comprises magnesium in amountsranging from 50 to 40,000 ppm, 50 to 20,000 ppm, 100 to 10,000 ppm, 200to 10,000 ppm, 500 to 5000 ppm, or 500 to 2500 ppm. In some embodiments,where Ca²⁺ and Mg²⁺ are both present, the ratio of Ca²⁺ to Mg²⁺ (i.e.,Ca²⁺:Mg²⁺) in the aqueous solution of divalent cations is 1:1 to 1:2.5;1:2.5 to 1:5; 1:5 to 1:10; 1:10 to 1:25; 1:25 to 1:50; 1:50 to 1:100;1:100 to 1:150; 1:150 to 1:200; 1:200 to 1:250; 1:250 to 1:500; or 1:500to 1:1000. In some embodiments, the ratio of Mg²⁺ to Ca²⁺ (i.e.,Mg²⁺:Ca²⁺) in the aqueous solution of divalent cations is 1:1 to 1:2.5;1:2.5 to 1:5; 1:5 to 1:10; 1:10 to 1:25; 1:25 to 1:50; 1:50 to 1:100;1:100 to 1:150; 1:150 to 1:200; 1:200 to 1:250; 1:250 to 1:500; or 1:500to 1:1000.

The aqueous solution of divalent cations may comprise divalent cationsderived from freshwater, brackish water, seawater, or brine (e.g.,naturally occurring brines or anthropogenic brines such as geothermalplant wastewaters, desalination plant waste waters), as well as othersalines having a salinity that is greater than that of freshwater, anyof which may be naturally occurring or anthropogenic. Brackish water iswater that is saltier than freshwater, but not as salty as seawater.Brackish water has a salinity ranging from about 0.5 to about 35 ppt(parts per thousand). Seawater is water from a sea, an ocean, or anyother saline body of water that has a salinity ranging from about 35 toabout 50 ppt. Brine is water saturated or nearly saturated with salt.Brine has a salinity that is about 50 ppt or greater. In someembodiments, the saltwater source from which divalent cations arederived is a naturally occurring source selected from a sea, an ocean, alake, a swamp, an estuary, a lagoon, a surface brine, a deep brine, analkaline lake, an inland sea, or the like. In some embodiments, thesaltwater source from which the divalent cations are derived is ananthropogenic brine selected from a geothermal plant wastewater or adesalination wastewater.

Freshwater is often a convenient source of divalent cations (e.g.,cations of alkaline earth metals such as Ca²⁺ and Mg²⁺). Any of a numberof suitable freshwater sources may be used, including freshwater sourcesranging from sources relatively free of minerals to sources relativelyrich in minerals. Mineral-rich freshwater sources may be naturallyoccurring, including any of a number of hard water sources, lakes, orinland seas. Some mineral-rich freshwater sources such as alkaline lakesor inland seas (e.g., Lake Van in Turkey) also provide a source ofpH-modifying agents. Mineral-rich freshwater sources may also beanthropogenic. For example, a mineral-poor (soft) water may be contactedwith a source of divalent cations such as alkaline earth metal cations(e.g., Ca²⁺, Mg²⁺, etc.) to produce a mineral-rich water that issuitable for methods and systems described herein. Divalent cations orprecursors thereof (e.g. salts, minerals) may be added to freshwater (orany other type of water described herein) using any convenient protocol(e.g., addition of solids, suspensions, or solutions). In someembodiments, divalent cations selected from Ca²⁺ and Mg²⁺ are added tofreshwater. In some embodiments, monovalent cations selected from Na⁺and K⁺ are added to freshwater. In some embodiments, freshwatercomprising Ca²⁺ is combined with magnesium silicates (e.g., olivine orserpentine), or products or processed forms thereof, yielding a solutioncomprising calcium and magnesium cations.

Many minerals provide sources of divalent cations and, in addition, someminerals are sources of base. Mafic and ultramafic minerals such asolivine, serpentine, and any other suitable mineral may be dissolvedusing any convenient protocol. Other minerals such as wollastonite mayalso be used. Dissolution may be accelerated by increasing surface area,such as by milling by conventional means or by, for example, jetmilling, as well as by use of, for example, ultrasonic techniques. Inaddition, mineral dissolution may be accelerated by exposure to acid orbase. Metal silicates (e.g., magnesium silicates) and other mineralscomprising cations of interest may be dissolved, for example, in acidsuch as HCl (optionally from an electrochemical process) to produce, forexample, magnesium and other metal cations for use in precipitationmaterial. In some embodiments, magnesium silicates and other mineralsmay be digested or dissolved in an aqueous solution that has becomeacidic due to the addition of carbon dioxide and other components ofwaste gas (e.g., combustion gas). Alternatively, other metal speciessuch as metal hydroxide (e.g., Mg(OH)2, Ca(OH)2) may be made availablefor use by dissolution of one or more metal silicates (e.g., olivine andserpentine) with aqueous alkali hydroxide (e.g., NaOH) or any othersuitable caustic material. Any suitable concentration of aqueous alkalihydroxide or other caustic material may be used to decompose metalsilicates, including highly concentrated and very dilute solutions. Theconcentration (by weight) of an alkali hydroxide (e.g., NaOH) insolution may be, for example, from 30% to 80% and from 70% to 20% water.Advantageously, metal silicates and the like digested with aqueousalkali hydroxide may be used directly to produce precipitation material.In addition, base value from the precipitation reaction mixture may berecovered and reused to digest additional metal silicates and the like.

In some embodiments, an aqueous solution of divalent cations may beobtained from an industrial plant that is also providing a combustiongas stream. For example, in water-cooled industrial plants, such asseawater-cooled industrial plants, water that has been used by anindustrial plant for cooling may then be used as water for producingprecipitation material. If desired, the water may be cooled prior toentering the precipitation system. Such approaches may be employed, forexample, with once-through cooling systems. For example, a city oragricultural water supply may be employed as a once-through coolingsystem for an industrial plant. Water from the industrial plant may thenbe employed for producing precipitation material, wherein output waterhas a reduced hardness and greater purity. If desired, such systems maybe modified to include security measures (e.g., to detect tampering suchas addition of poisons) and coordinated with governmental agencies(e.g., Homeland Security or other agencies). Additional tampering orattack safeguards may be employed in such embodiments.

Proton-Removing Agents and Methods

As disclosed above, waste sources of metal oxides such as combustion ash(e.g., fly ash, bottom ash, boiler slag), cement kiln dust, and slag(e.g. iron slag, phosphorous slag), each of which is described in moredetail in a respective section below, may be the sole source ofproton-removing agents for preparation of the compositions describedherein; however, waste sources such as ash, cement kiln dust, slag (e.g.iron slag, phosphorous slag) may also be used in combination withsupplemental sources of proton-removing agents (and methods foreffecting proton removal) as described in this section.

Methods of the invention include contacting a volume of an aqueoussolution of divalent cations with a source of CO2 (to dissolve CO2) andsubjecting the resultant solution to precipitation conditions. Thedissolution of CO2 into the aqueous solution of divalent cationsproduces carbonic acid, a species in equilibrium with both bicarbonateand carbonate. In order to produce carbonate-containing precipitationmaterial, protons are removed from various species (e.g. carbonic acid,bicarbonate, hydronium, etc.) in the divalent cation-containing solutionto shift the equilibrium toward carbonate. As protons are removed, moreCO2 goes into solution. In some embodiments, proton-removing agentsand/or methods are used while contacting a divalent cation-containingaqueous solution with CO2 to increase CO2 absorption in one phase of theprecipitation reaction, where the pH may remain constant, increase, oreven decrease, followed by a rapid removal of protons (e.g., by additionof a base) to cause rapid precipitation of carbonate-containingprecipitation material. Protons may be removed from the various species(e.g. carbonic acid, bicarbonate, hydronium, etc.) by any convenientapproach, including, but not limited to use of naturally occurringproton-removing agents, use of microorganisms and fungi, use ofsynthetic chemical proton-removing agents, recovery of man-made wastestreams, and using electrochemical means.

Naturally occurring proton-removing agents encompass any proton-removingagents that can be found in the wider environment that may create orhave a basic local environment. Some embodiments provide for naturallyoccurring proton-removing agents including minerals that create basicenvironments upon addition to solution (i.e., dissolution). Suchminerals include, but are not limited to lime (CaO); periclase (MgO);volcanic ash; ultramafic rocks and minerals such as serpentine; and ironhydroxide minerals (e.g., goethite and limonite). Methods of dissolutionof such rocks and minerals are provided herein. Some embodiments providefor using naturally alkaline bodies of water as naturally occurringproton-removing agents. Examples of naturally alkaline bodies of waterinclude, but are not limited to surface water sources (e.g. alkalinelakes such as Mono Lake in California) and ground water sources (e.g.basic aquifers). Other embodiments provide for use of deposits fromdried alkaline bodies of water such as the crust along Lake Natron inAfrica's Great Rift Valley. In some embodiments, organisms that excretebasic molecules or solutions in their normal metabolism are used asproton-removing agents. Examples of such organisms are fungi thatproduce alkaline protease (e.g., the deep-sea fungus Aspergillus ustuswith an optimal pH of 9) and bacteria that create alkaline molecules(e.g., cyanobacteria such as Lyngbya sp. from the Atlin wetland inBritish Columbia, which increases pH from a byproduct ofphotosynthesis). In some embodiments, organisms are used to produceproton-removing agents, wherein the organisms (e.g., Bacilluspasteurizing, which hydrolyzes urea to ammonia) metabolize a contaminant(e.g. urea) to produce proton-removing agents or solutions comprisingproton-removing agents (e.g., ammonia, ammonium hydroxide). In someembodiments, organisms are cultured separately from the precipitationreaction mixture, wherein proton-removing agents or solution comprisingproton-removing agents are used for addition to the precipitationreaction mixture. In some embodiments, carbonic anhydrase is used as anaturally occurring proton-removing agent for removing protons to invokeprecipitation of precipitation material. Carbonic anhydrase, which is anenzyme produced by plants and animals, accelerates transformation ofcarbonic acid to bicarbonate in aqueous solution.

Chemical agents for effecting proton removal generally refer tosynthetic chemical agents that are produced in large quantities and arecommercially available. For example, chemical agents for removingprotons include, but are not limited to, hydroxides, organic bases,super bases, oxides, ammonia, and carbonates. Hydroxides includechemical species that provide hydroxide anions in solution, including,for example, sodium hydroxide (NaOH), potassium hydroxide (KOH), calciumhydroxide (Ca(OH)2), or magnesium hydroxide (Mg(OH)2). Organic bases arecarbon-containing molecules that are generally nitrogenous basesincluding primary amines such as methyl amine, secondary amines such asdiisopropylamine, tertiary such as diisopropylethylamine, aromaticamines such as aniline, heteroaromatics such as pyridine, imidazole, andbenzimidazole, and various forms thereof. In some embodiments, anorganic base selected from pyridine, methylamine, imidazole,benzimidazole, histidine, and a phophazene is used to remove protonsfrom various species (e.g., carbonic acid, bicarbonate, hydronium, etc.)for precipitation of precipitation material. In some embodiments,ammonia is used to raise pH to a level sufficient to precipitateprecipitation material from a solution of divalent cations and anindustrial waste stream. Super bases suitable for use as proton-removingagents include sodium ethoxide, sodium amide (NaNH2), sodium hydride(NaH), butyl lithium, lithium diisopropylamide, lithium diethylamide,and lithium bis(trimethylsilyl)amide. Oxides including, for example,calcium oxide (CaO), magnesium oxide (MgO), strontium oxide (SrO),beryllium oxide (BeO), and barium oxide (BaO) are also suitableproton-removing agents that may be used. Carbonates for use in theinvention include, but are not limited to, sodium carbonate.

In addition to comprising cations of interest and other suitable metalforms, waste streams from various industrial processes may provideproton-removing agents. Such waste streams include, but are not limitedto, mining wastes; fossil fuel burning ash (e.g., fly ash, as describedin further detail herein); slag (e.g. iron slag, phosphorous slag);cement kiln waste; oil refinery/petrochemical refinery waste (e.g. oilfield and methane seam brines); coal seam wastes (e.g. gas productionbrines and coal seam brine); paper processing waste; water softeningwaste brine (e.g., ion exchange effluent); silicon processing wastes;agricultural waste; metal finishing waste; high pH textile waste; andcaustic sludge. Mining wastes include any wastes from the extraction ofmetal or another precious or useful mineral from the earth. In someembodiments, wastes from mining are used to modify pH, wherein the wasteis selected from red mud from the Bayer aluminum extraction process;waste from magnesium extraction from sea water (e.g., Mg(OH)2 such asthat found in Moss Landing, Calif.); and wastes from mining processesinvolving leaching. For example, red mud may be used to modify pH asdescribed in U.S. Provisional Patent Application 61/161,369, filed 18Mar. 2009, which is hereby incorporated by reference in its entirety.Agricultural waste, either through animal waste or excessive fertilizeruse, may contain potassium hydroxide (KOH) or ammonia (NH3) or both. Assuch, agricultural waste may be used in some embodiments of theinvention as a proton-removing agent. This agricultural waste is oftencollected in ponds, but it may also percolate down into aquifers, whereit can be accessed and used.

Electrochemical methods are another means to remove protons from variousspecies in a solution, either by removing protons from solute (e.g.,deprotonation of carbonic acid or bicarbonate) or from solvent (e.g.,deprotonation of hydronium or water). Deprotonation of solvent mayresult, for example, if proton production from CO2 dissolution matchesor exceeds electrochemical proton removal from solute molecules.Alternatively, electrochemical methods may be used to produce causticmolecules (e.g., hydroxide) through, for example, the chlor-alkaliprocess, or modification thereof. Electrodes (i.e., cathodes and anodes)may be present in the apparatus containing the divalentcation-containing aqueous solution or gaseous waste stream-charged(e.g., CO2-charged) solution, and a selective barrier, such as amembrane, may separate the electrodes. Electrochemical systems andmethods for removing protons may produce by-products (e.g., hydrogen)that may be harvested and used for other purposes. Additionalelectrochemical approaches that may be used in systems and methods ofthe invention include, but are not limited to, those described in U.S.61/081,299 and U.S. 61/091,729, the disclosures of which are hereinincorporated by reference.

In some embodiments, low-voltage electrochemical methods are used toremove protons, for example, as CO2 is dissolved in the precipitationreaction mixture or a precursor solution to the precipitation reactionmixture. A precursor solution to the precipitation mixture, for example,may or may not contain divalent cations. In some embodiments, CO2dissolved in an aqueous solution that does not contain divalent cationsis treated by a low-voltage electrochemical method to remove protonsfrom carbonic acid, bicarbonate, hydronium, or any species orcombination thereof resulting from the dissolution of CO2. A low-voltageelectrochemical method operates at an average voltage of 2, 1.9, 1.8,1.7, or 1.6 V or less, such as 1.5, 1.4, 1.3, 1.2, 1.1 V or less, suchas 1 V or less, such as 0.9 V or less, 0.8 V or less, 0.7 V or less, 0.6V or less, 0.5 V or less, 0.4 V or less, 0.3 V or less, 0.2 V or less,or 0.1 V or less. Low-voltage electrochemical methods that do notgenerate chlorine gas are convenient for use in systems and methods ofthe invention. Low-voltage electrochemical methods to remove protonsthat do not generate oxygen gas are also convenient for use in systemsand methods of the invention. In some embodiments, low-voltageelectrochemical methods generate hydrogen gas at the cathode andtransport it to the anode where the hydrogen gas is converted toprotons. Electrochemical methods that do not generate hydrogen gas mayalso be convenient. In some instances, electrochemical methods to removeprotons do not generate any gaseous by-byproduct. See, for example, U.S.patent application Ser. No. 12/344,019, filed Dec. 24, 2008, U.S. patentapplication Ser. No. 12/375,632, filed Dec. 23, 2008, PCT ApplicationNo. PCT/US08/088242, filed Dec. 23, 2008, and PCT Application No.PCT/US09/32301, filed Jan. 28, 2009, all of which are herebyincorporated by reference in their entirety.

Combustion Ash, Cement Kiln Dust, and Slag

A waste source of metal oxides (e.g., combustion ashes such as fly ash,cement kiln dust, etc.) may be the sole sources of proton-removingagents for preparation of compositions described herein. In other words,a waste source of metal oxides such as combustion ash, cement kiln dust,or the like may provide the sole source of proton-removing agents usedto modify the pH of the reaction mixture from which compositions of theinvention are produced. As such, in some embodiments, the sole source ofproton-removing agents is a combustion ash selected from fly ash, bottomash, and boiler slag. In some embodiments, the sole source ofproton-removing agent is cement kiln dust. In some embodiments, the solesource of proton-removing agent is slag (e.g. iron slag, phosphorousslag). Likewise, a waste source of metal oxides (e.g., combustion ashessuch as fly ash, cement kiln dust, etc.) may be the sole source ofdivalent metal cations for preparation of compositions described herein.In other words, a waste source of metal oxides such as combustion ash,cement kiln dust, or the like may provide the sole source of divalentcations from which compositions of the invention are produced. As such,in some embodiments, the sole source of divalent cations is a combustionash selected from fly ash, bottom ash, and boiler slag. In someembodiments, the sole source of divalent cations is cement kiln dust. Insome embodiments, the sole source of divalent cations is slag (e.g. ironslag, phosphorous slag). A waste source of metal oxides (e.g.,combustion ash such as fly ash, cement kiln dust, etc.), in someembodiments, provides the sole source of divalent cations andproton-removing agents for precipitation of precipitation material inaccordance with the invention. For example, fly ash may provide bothdivalent cations and proton-removing agents for precipitation ofprecipitation material. In addition, combinations of waste sources ofmetal oxides and other sources of either divalent cations and/orproton-removing agent are discussed in further detail herein.

Carbon-based fuels such as coal generate combustion ash waste productssuch as fly ash, bottom ash, and boiler slag which are often landfilled, or utilized in low-value applications as a means of disposal.These waste products often contain leachable pollutants, which cancontaminate the groundwater when land filled. The American Coal AshAssociation reports that more than 56% of the 165,000,000 tons of coalcombustion products generated in the United States annually are simplysent to a landfill at substantial costs to coal-burning entities.Combustion ash resulting from burning fossil fuels (e.g., coal incoal-fired power plants) is often rich in CaO or other metal oxides thatcreate a basic environment and provide divalent cations in solution.Combustion products from coal, wood, and other sources, includingvolcanic ash released in volcano eruptions, each of which is generallyconsidered a combustion ash, may also contain various oxides such assilica (SiO2), alumina (Al2O3), and oxides of calcium, magnesium, iron,and the like, which may enhance certain chemical reactions and resultantcements. Coal ash (i.e., combustion ash resulting from burning coal) asemployed in this invention refers to ash materials produced in powerplant boilers or coal burning furnaces (e.g., chain grate boilers,dry-bottom pulverized coal boilers, slag-tap boilers, cyclone boilers,and fluidized bed boilers) from burning pulverized anthracite, lignite,bituminous, sub-bituminous, or brown coal. Such coal ash includes flyash, which is the finely divided coal ash carried from the furnace byexhaust or flue gases; bottom ash, which collects at the base of thefurnace as agglomerates (e.g., in a dry-bottom boiler); and boiler slag,which collects in the ash hopper of a wet-bottom boiler.

High-sulfur coals, which are abundant and relatively lower in cost thanlow-sulfur coals, generally require Flue Gas Desulfurization (FGD) toremove sulfur oxides (“SOx”) from flue gas emissions. This processgenerally further releases CO2 into the atmosphere by utilizinglimestone as a reactant to produce CaSO4 (gypsum). This process produceshigh calcium fly ash due to the calcium released from the limestone inthe process, where the calcium is in the form of calcium oxide (CaO).Pretreatment of flue gas prior to atmospheric release in normal powerplants or industrial coal-burning facilities may include processes suchas electrostatic precipitation (“ESP”), wet or dry scrubbing, and a fluegas desulfurization (“FGD”). In many FGD processes, the flue gas, afterundergoing ESP, is brought into an FGD absorber tank, where it isreacted with a limestone slurry to form CaSO4 and remove sulfur from theflue gas. Each molecule of CaSO4 formed in this manner releases amolecule of CO2, further exacerbating the high release of CO2 associatedwith burning of fossil fuels such as coal.

Fly ashes are generally highly heterogeneous, and include of a mixtureof glassy particles with various identifiable crystalline phases such asquartz, mullite, hematite, magnetite, and various iron oxides inaddition. Fly ashes of interest include Type F and Type C fly ash. TheType F and Type C fly ashes referred to above are defined by CSAStandard A23.5 and ASTM C618. The chief difference between these classesis the amount of calcium, silica, alumina, and iron content in the ash.The chemical properties of the fly ash are largely influenced by thechemical content of the coal burned (e.g., anthracite, bituminous,sub-bituminous, lignite, brown). The properties of the fly ash may alsodepend upon temperature history, the type of burner used, post-burntreatment, scrubber effects, and impounding time and conditions. Flyashes of interest include substantial amounts of silica (silicondioxide, SiO2) (both amorphous and crystalline) and lime (calcium oxide,CaO, magnesium oxide, MgO). The outer surface of fly ash is generallyrich in CaO and MgO with concentrations of CaO and MgO decreasing fromthe outer surface of fly ash toward the center. With the decrease in CaOand MgO, there is a concomitant increase in the concentration of SiO2.High shear mixing and wet milling, which are used in some embodimentsdescribed below, allow for greater access to the entire CaO and MgOstock present in fly ash. Table 1 below provides the chemical makeup ofvarious types of fly ash that find use in embodiments of the invention.

TABLE 1 Coal types and composition. Component Bituminous Sub-bituminousLignite Brown SiO₂ (%) 20-60 40-60  15-45 5-30 Al₂O₃ (%)  5-35 20-30 20-25 1-20 Fe₂O₃ (%) 10-40 4-10  4-15 5-50 CaO (%)  1-12 5-30 15-40 5-30MgO (%) 1-5 1-10  1-10 5-30

The burning of harder, older anthracite and bituminous coal typicallyproduces Class F fly ash. Class F fly ash is pozzolanic in nature (i.e.,in the presence of moisture, finely divided silica or aluminosilicatesreact with Ca(OH)2 to form compounds having cementitious properties,wherein the silica or aluminosilicates alone have little to nocementitious properties), and contains less than 10% lime (CaO). Fly ashproduced from the burning of younger lignite or sub-bituminous coal, inaddition to having pozzolanic properties, also has some self-cementingproperties. In the presence of water, Class C fly ash will harden andgain strength over time. Class C fly ash generally contains more than20% lime (CaO). Alkali and sulfate (SO4) contents are generally higherin Class C fly ashes.

Fly ash material solidifies while suspended in exhaust gases and iscollected using various approaches, for example, by electrostaticprecipitators or filter bags. Since the particles solidify whilesuspended in the exhaust gases, fly ash particles are generallyspherical in shape and range in size from 0.5 μm to 100 μm. Fly ashes ofinterest include those in which at least about 80%, by weight comprisesparticles of less than 45 microns.

Also of interest in certain embodiments of the invention is the use ofhighly alkaline fluidized bed combustor (FBC) fly ash.

Also of interest in embodiments of the invention is the use of bottomash. Bottom ash is formed as agglomerates in coal combustion boilersfrom the combustion of coal. The agglomerates have a size in which 90%of the agglomerates fall within the particle size range of 0.1 mm to 20mm, and where the bottom ash agglomerates have a wide distribution ofagglomerate size within this range. Combustion boilers may be wet bottomboilers or dry bottom boilers. When produced in a wet-bottom boiler, thebottom ash is quenched with water producing boiler slag. The mainchemical components of a bottom ash are silica and alumina with lesseramounts of oxides of Fe, Ca, Mg, Mn, Na and K, as well as sulfur andcarbon.

Also of interest in certain embodiments is the use of volcanic ash asthe ash. Volcanic ash is made up of small tephra, (i.e., bits ofpulverized rock and glass created by volcanic eruptions) less than 2millimeters (0.079 in) in diameter.

Cement kiln dust is also useful as a waste source of metal oxides,providing, for example, CaO and MgO that may be used as both a divalentcation source and as a proton-removing agent source.

Cement kiln dust, which is a fine by-product of cement productioncaptured in a dust collection system (e.g., cyclones, electrostaticprecipitators, bughouses, etc.), may be classified into one of fourcategories, each of which is suitable for use as a waste source of metaloxides for the invention. The four categories are based upon twodifferent cement kiln processes and two different dust collectionprocesses. With this in mind, cement kiln dust from wet-process kilnprocesses, which accept feed materials in a slurry form, and dry-processkiln processes, which accept feed materials in a dry, ground form aresuitable for use in the invention. In each type of kiln, the dust may becollected in two ways: a portion of the dust may be separated andreturned to the kiln from the dust collection system (e.g., cyclone)closest to the kiln, or the total quantity of dust produced may berecycled or discarded. Cement kiln dust obtained from either type ofcollection system is suitable for use in the invention.

The chemical and physical characteristics of cement kiln dust greatlydepend upon the dust collection method employed at the cement productionfacility. Chemically, cement kiln dust has a composition similar toconventional Portland cement. The principal constituents of cement kilndust are compounds of lime, iron, silica, and alumina. The concentrationof free lime in cement kiln dust is highest in coarser particlescaptured closest to the kiln. As such, coarser particles with higherconcentrations of free lime are particularly suited for methods andsystems of the invention; however, finer particles of cement kiln dust,which tend to exhibit a higher concentration of sulfates and/or alkalisare also suited for the invention as finer particles also contain usefulconcentrations of, for example, CaO. In systems in which coarserparticles of cement kiln dust are not separated out and returned to thekiln, the total dust will be higher in free lime (since it will containsome coarse particles). This cement kiln dust may also be used as awaste source of metal oxides, providing divalent cations andproton-removing agents. As evidenced by Table 2 (Collins, R. J. and J.J. Emery. Kiln Dust-Fly Ash Systems for Highway Bases and Subbases.Federal Highway Administration, Report No. FHWA/RD-82/167, Washington,D.C., September, 1983.), which lists typical compositions for fresh andstockpiled cement kiln dust, there is very little, if any, free lime orfree magnesia content in cement kiln dust that has been stockpiled andexposed to the environment for long periods. As such, cement kiln dustthat is fresh is preferred over cement kiln dust that has beenstockpiled for any significant length of time in the environment.

TABLE 2 Typical chemical compositions of cement kiln dust. ChemicalStockpiled (%) Species Fresh (%) Sample 1 Sample 2 CaO 40.5 31.4 44.2Free Lime 4.4 0.0 0.0 SiO2 14.5 11.7 11.9 Al2O3 4.10 3.18 3.24 MgO 1.550.97 1.73 Na2O 0.44 0.13 0.27 K2O 4.66 1.65 2.92 Fe2O3 2.00 2.16 1.45SO₃ 6.50 8.24 2.40 Loss On 22.9 40.4 30.2 Ignition, 105° C.

Slag may also be employed as a proton-removing agent (as well as asource divalent cations) to increase the pH of, for example,precipitation reaction mixture charged with CO2. Slag may be used as asole proton-removing agent or in conjunction with one or more additionalproton-removing agents (e.g., other waste sources of metal oxides,supplemental proton-removing agents described above, etc). Likewise,slag may be used as a sole source of divalent cations or in conjunctionwith one or more additional sources of divalent cations (e.g., otherwaste sources of metal oxides, supplemental sources of divalent cationsdescribed above, etc). Slag is generated from the processing of metalore (i.e., smelting metal ors to purify metals), and may contain calciumand magnesium oxides as well as iron, silicon, and aluminum compounds.In some embodiments, the use of slag as a proton-removing agent ordivalent cation source provides additional benefits through theintroduction of reactive silicon and alumina to the precipitatedproduct. Slags that may be suitable for the invention include, but arenot limited to, blast furnace slag from iron smelting, slag fromelectric-arc or blast furnace processing of steel, copper slag, nickelslag, and phosphorus slag.

Additives

Additives other than proton-removing agents may be added to theprecipitation reaction mixture in order to influence the nature of theprecipitation material that is produced. As such, in some embodiments,an additive is provided to the precipitation reaction mixture before orduring the time when the precipitation reaction mixture is subjected tothe precipitation conditions. Certain calcium carbonate polymorphs arefavored by trace amounts of certain additives. For example, vaterite, ahighly unstable polymorph of CaCO3, which precipitates in a variety ofdifferent morphologies and rapidly converts to calcite, may be obtainedin very high yields by including trace amounts of lanthanum as, forexample, lanthanum chloride. Other transition metals and the like may beadded to produce calcium carbonate polymorphs. For instance, theaddition of ferrous or ferric iron is known to favor the formation ofdisordered dolomite (protodolomite).

Methods

Methods and systems of the invention provide carbonate-containingcompositions that may be prepared from an aqueous solution comprisingdissolved carbon dioxide (e.g., form an industrial waste streamcomprising CO2), divalent cations (e.g., Ca²⁺, Mg²⁺), andproton-removing agents (or methods of effecting proton removal) asdescribed in more detail below.

A waste source of metal oxides such as combustion ash (e.g., fly ash,bottom ash, boiler slag), cement kiln dust, or slag (e.g. iron slag,phosphorous slag) may be the sole source of divalent metal cations forpreparation of the compositions described herein. As such, in someembodiments, the sole source of divalent metal cations is a combustionash selected from fly ash, bottom ash, and boiler slag. In someembodiments, the sole source of divalent metal cations is cement kilndust. In some embodiments, the sole source of divalent metal cations isslag (e.g. iron slag, phosphorous slag). A waste source of metal oxidessuch as combustion ash (e.g., fly ash, bottom ash, boiler slag), cementkiln dust, or slag (e.g. iron slag, phosphorous slag) may also be thesole source of proton-removing agents for preparation of thecompositions described herein. As such, in some embodiments, the solesource of proton-removing agents is a combustion ash selected from flyash, bottom ash, and boiler slag. In some embodiments the sole source ofproton-removing agents is cement kiln dust. In some embodiments, thesole source of proton-removing agents is slag (e.g. iron slag,phosphorous slag). In some embodiments, mineral content in water isachieved by enriching the water source with divalent cations by adding awaste source of metal oxides such as combustion ash (e.g., fly ash,bottom ash, boiler slag), cement kiln dust, or slag (e.g. iron slag,phosphorous slag) to fresh or distilled water, wherein the fresh ordistilled water have low or no mineral content. In these embodiments,the waste source of metal oxides provides not only divalent cations, butalso a source proton-removing agents.

In some embodiments, a waste source of metal oxides provides a portionof the proton-removing agents, such as 10% or less, 20% or less, 40% orless, 60% or less, 80% or less, with the remaining portion ofproton-removing agents (or methods of effecting proton removal) providedas described herein.

Water may be contacted with a waste source of metal oxides such ascombustion ash (e.g., fly ash) or cement kiln dust to achieve a desiredpH (by means of proton-removing agent addition) or divalent cationconcentration using any convenient protocol. In some embodiments, fluegas from a coal-fired power plant is passed directly into aprecipitation reactor without prior removal of the fly ash, obviatingthe use of electrostatic precipitators and the like. In someembodiments, cement kiln dust is provided to a precipitation reactordirectly from the cement kiln. In some embodiments, previously collectedfly ash may be placed in a precipitation reactor holding water, whereinthe amount of fly ash added is sufficient to raise the pH to a desiredlevel (e.g., a pH that induces precipitation of carbonate-containingprecipitation material) such as pH 7-14, pH 8-14, pH 9-14, pH 10-14, pH11-14, pH 12-14, or pH 13-14. The pH of fly ash-water mixtures, forexample, may be about pH 12.2-12.4. The pH of cement kiln dust-watermixtures may be about pH 12 as well. In some embodiments, the wastesource of metal oxides is immobilized in a column or bed. In suchembodiments, water is passed through or over an amount of the ashsufficient to raise the pH of the water to a desired pH or to aparticular divalent cation concentration. Immobilized waste sources ofmetal oxides (e.g., fly ash) are useful in mitigating passivation of flyash (i.e., encapsulation of fly ash by, for example, CaCO3 as CaCO3forms under precipitation conditions); however, in some embodiments,passivation of fly ash is desirable as precipitation material comprisingpassivated fly ash has a reduced pozzolanic reactivity (i.e., reactionof silica and/or aluminosilica with Ca(OH)2), which may allow foradditional uses in which less reactivity is desired. As both cement kilndust and combustion ashes such as fly ash comprise significant basevalue, they are considered to be fairly caustic. Additional base and ordivalent cation value may be obtained from waste source-water mixturesby removing the base and/or divalent cation value. For example, thewaste source-water mixture may be contacted with a CO2 source (whichforms carbonic acid in solution) to form precipitation materialcomprising calcium carbonates, the formation of which allows foradditional conversion of CaO into Ca(OH)2 and additional divalentcations. Likewise, the waste source-water mixture may be contacted withaqueous acids such as, but not limited to, HNO3, HCl, and HF. Aciddigestion of fly ash with acids such as HNO3 and HCl allows greateraccess (70% or more) to CaO and MgO present in the fly ash. Aciddigestion with aqueous HF allows for greater access to CaO and MgOthrough reaction with silica and dissolution of the resultant species.Reaction time and acid strength may be varied to increase or decreasethe amount of CaO and/or MgO is leached from fly ash.

A waste source of metal oxides such as fly ash or cement kiln dust mayalso be slaked (i.e., conversion of CaO to Ca(OH)2, MgO to Mg(OH)2,etc.) in some embodiments. Any convenient system or method may be usedto effect slaking of combustion ashes (e.g., fly ash, bottom ash) orcement kiln dust. Slaking waste sources of metal oxides may be achievedwith, for example, a slurry detention slacker, a paste slaker, a ballmill slaker, or any combinations or variations thereof, the choice ofslaking apparatus depending upon the waste source of metal oxides to beslaked, availability of water, space requirements, etc. For example, ifspace is limited and water for slaking is in limited supply, a compactpaste slaker may be convenient for use in systems and methods of theinvention. In some embodiments, a ball mill slaker is used. Slakingefficiency, depending on the waste source of metal oxides, may beaffected by factors including the type of limestone used forcalcination, the particular calcination process (e.g., temperaturehistory, type of burner used, post-burn treatment, scrubber effects,impounding time and conditions, etc.), the slaking temperature, thewaste source to water ratio, the degree of agitation during slaking, theslurry viscosity, the slaking time, and the water temperature (prior tomixing with the waste source of metal oxide). The type of water may alsohave an effect on slaking efficiency. For example, freshwater, whichgenerally has a lower concentration of divalent cations than inseawater, may be far more efficient at extracting CaO and MgO from flyash; however, the type of water will generally depend on availability atthe precipitation plant location. As such, methods of the inventioninclude modification of these factors for timely slaking (i.e., slakingon a timescale which allows for an efficient industrial process).Slaking temperature, for example, may be modified. In some embodiments,the slaking temperature ranges from room temperature (about 70° F.) toabout 220° F. In some embodiments, the slaking temperature is 70-100°F., 100-220° F., 120-220° F., 140-220° F., 160-220° F., 160-200° F., or160-185° F. Should auxiliary heat be needed to increase slakingtemperature (beyond that resulting from the exothermic conversion of CaOto Ca(OH)2), waste heat from, for example, flue gas may be used. Otherexternal sources of heat (e.g., heated water) may be used as well.Should slaking temperature need to be decreased due to highly reactivewaste sources of metal oxides (i.e., fly ash or cement kiln dustcomprising high concentrations, for example, CaO), the heat may be usedto, for example, heat an air stream for use in drying precipitationmaterial. Slaking pressure, for example, may be modified. In someembodiments, the slaking pressure is normal atmospheric pressure (about1 bar) to about 50 bar. In some embodiments, the slaking pressure is1-2.5 bar, 1-5 bar, 1-10 bar, 10-50 bar, 20-50 bar, 30-50 bar, or 40-50bar. In some embodiments, slaking is performed under ambient conditions(i.e., normal atmospheric temperature and pressure). Water to wastesource ratio may be modified. In some embodiments, the ratio of water tothe waste source of metal oxides is 1:1 to 1:1.5; 1:1.5 to 1:2; 1:2 to1:2.5; 1:2.5 to 1:3; 1:3 to 1:3.5; 1:3.5 to 1:4; 1:4 to 1:4.5; 1:4.5 to1:5; 1:5 to 1:6; 1:6 to 1:8; 1:8 to 1:10; 1:10 to 1:25; 1:25 to 1:50; or1:50 to 1:100. Waste source to water ratio may also be modified. In someembodiments, the ratio of the waste source of metal oxides to water is1:1 to 1:1.5; 1:1.5 to 1:2; 1:2 to 1:2.5; 1:2.5 to 1:3; 1:3 to 1:3.5;1:3.5 to 1:4; 1:4 to 1:4.5; 1:4.5 to 1:5; 1:5 to 1:6; 1:6 to 1:8; 1:8 to1:10; 1:10 to 1:25; 1:25 to 1:50; or 1:50 to 1:100. In some embodiments,where a waste source of metal oxides such as fly ash is directlyprovided to a precipitation reactor, the waste source to water ratio maybe quite low. In such embodiments, additional waste source (e.g., flyash) may be added to the precipitation reactor to increase the wastesource to water ratio or slaking may be performed with the low ratio ofwaste source to water. Slaking time may also be modified as it has aneffect on slaking efficiency. In some embodiments, the slaking timerequired to complete hydration (e.g., formation of Ca(OH)2 from CaO) isbetween 12 and 20 hours, between 20 and 30 hours, between 30 and 40hours, between 40 and 60 hours, between 60 and 100 hours, between 100and 160, between 100 and 180, and between 180 and 200 hours. In someembodiments, the slaking time required to complete hydration is lessthan 12 hours, between 6 and 12 hours, between 3 and 6 hours, between 1and 3 hours, or less than 1 hour. In some embodiments, the slaking timerequired to complete hydration is between 30 minutes and 1 hour. In someembodiments, the slaking time is between 15 and 30 minutes, 15 and 25minutes, and 15 and 20 minutes. In some embodiments, the slaking time isbetween 5 and 30 minutes, 5 and 20 minutes, 5 and 15 minutes, and 5 and10 minutes. In some embodiments, the slaking time is between 1 and 5minutes, 1 and 3 minutes, and 2 and 3 minutes. Agitation may also beused to effect slaking efficiency, for example, by eliminating hot andcold spots. In addition, pretreatment of the waste source of metaloxides may be used to effect slaking efficiency. For example, fly ashmay be jet milled or ball milled before slaking. It will be recognizedthat changing any one of the described slaking factors may changeadditional slaking factors such that each slaking procedure, dependingupon available materials, will be different. As such, slaking inaccordance with the invention may result in more than 10%, more than20%, more than 30%, more than 40%, more than 50%, more than 60%, morethan 70%, more than 80%, more than 90%, more than 95%, more than 97%,more than 98%, more than 99%, or more than 99.9% conversion of CaOpresent in the waste source to Ca(OH)2. Likewise, slaking in accordancewith the invention may result in more than 10%, more than 20%, more than30%, more than 40%, more than 50%, more than 60%, more than 70%, morethan 80%, more than 90%, more than 95%, more than 97%, more than 98%,more than 99%, or more than 99.9% conversion of MgO present in the wastesource to Mg(OH)2. The higher the conversion, the higher the efficiencyof the slaking process.

A waste source of metal oxides such as combustion ash, cement kiln dust,or slag (e.g. iron slag, phosphorous slag), may also be used incombination with supplemental sources of divalent cations, includingmixtures of combustion ash, cement kiln dust, or slag (e.g. iron slag,phosphorous slag). As such, in some embodiments, the source of divalentcations is a combination of a divalent cation source and a combustionash selected from fly ash, bottom, ash, and boiler slag. For example,the source of divalent cations may be a combination of fly ash andseawater. When a combination (e.g., combustion ash in combination withanother source of divalent cations) is used, the combustion ash may beused in any order. For example, a basic solution may already containdivalent cations (e.g., seawater) before adding a combustion ash, or asource of divalent cations may be added to a slurry of fly ash in water.In any of these embodiments, as described in further detail below, CO2is added before or after combustion ash.

A waste source such as combustion ash, cement kiln dust, or slag (e.g.iron slag, phosphorous slag), may be used in combination withsupplemental sources of proton-removing agents, including mixtures ofcombustion ash, cement kiln dust, or slag (e.g. iron slag, phosphorousslag). As such, in some embodiments, the source of proton-removingagents is a combination of a proton-removing agent and a combustion ashselected from fly ash, bottom ash, and boiler slag. Examples ofproton-removing agents that may be used include oxides (e.g., CaO),hydroxides (e.g., KOH, NaOH, brucite (Mg(OH)2, etc.), carbonates (e.g.,Na2CO3), serpentine, and the like. Serpentine, which also releasessilica and magnesium into the reaction mixture, ultimately leads tocompositions comprising carbonates and silica (in addition to that foundin combustion ashes). The amount of supplemental proton-removing agentthat is used depends upon the particular nature of the supplementalproton-removing agent and the volume of water to which the supplementalproton-removing agent is being added. An alternative to supplementalproton-removing agents is use of electrochemical methods such as thosedescribed above to effect proton removal. Electrolysis may also beemployed. Different electrolysis processes may be used, including theCastner-Kellner process, the diaphragm cell process, and the membranecell process. By-products of the hydrolysis product (e.g., H2, sodiummetal) may be collected and employed for other purposes. When acombination of proton removing agents (e.g., combustion ash incombination with another proton-removing agent source) is used, thecombustion ash may be used in any order. For example, a divalentcation-containing solution may already be basic (e.g., seawater) beforeadding a combustion ash, or a slurry of fly ash in water may be furtherbasicified through addition of an additional proton-removing agent. Inany of these embodiments, as described in more detail below, CO2 isadded before or after combustion ash.

As described above, waste sources of metal oxides such as combustionash, cement kiln ash, and slag (e.g. iron slag, phosphorous slag) may beused in various combinations, both with and without supplementalproton-removing agents. When supplemental proton-removing agents (andmethods effecting proton removal) are used, the supplementalproton-removing agents too may be used in any suitable combination. Someembodiments of the invention provide for combinations including use ofanthropogenic waste (e.g., red mud or brown mud from bauxite processing)in combination with commercially available base (e.g., NaOH);anthropogenic waste in combination with electrochemical methods (i.e.,deprotonation of carbonic acid, bicarbonate, hydronium, etc.) andnaturally occurring proton-removing agents (e.g. serpentine minerals);or anthropogenic waste in combination with commercially available baseand naturally occurring proton-removing, followed by a transition toserpentine minerals combined with electrochemical methods. Theproportion of the various methods for effecting proton removal may beadjusted according to conditions and availability, for example,anthropogenic waste may be used in combination with commerciallyavailable base and naturally occurring proton-removing agents for thefirst five years of a precipitation plant's life-time, followed by atransition to serpentine minerals combined with electrochemical methodsfor removing protons as these become more available.

In some embodiments, proton-removing agents (and methods for effectingproton removal) are combined such that 1-30% of the proton-removingagent is sourced from fly ash, 20-80% of the proton-removing agent issourced from waste (e.g. red mud), minerals such as serpentine, or acombination thereof, and 10-50% of proton removal is effected throughelectrochemical methods. For example, some embodiments provide for acombination of proton-removing agents and electrochemical methods suchthat 10% of the proton-removing agent is sourced from fly ash, 60% ofthe proton-removing agent is sourced from waste from a mining process(e.g. red mud), and 30% of the proton removal is effected byelectrochemical methods. Some embodiments provide for a combination ofproton-removing agents and electrochemical methods such that 10% of theproton-removing agent is sourced from fly ash, 60% of theproton-removing agent is from sourced from naturally occurring mineralsources (e.g. dissolved serpentine), and 30% of the proton removal iseffected by electrochemical methods. Some embodiments provide for acombination of proton-removing agents and electrochemical methods suchthat 30% of the proton-removing agent is sourced from fly ash and 70% ofthe proton-removing agent is sourced from waste from a mining process(e.g. red mud) for the first five years of a precipitations plant'slife-time, and from the beginning of the sixth year onward, such that10% of the proton-removing agent is sourced from fly ash, 60% of theproton-removing agent is the result of the dissolution of a naturallyoccurring mineral source (e.g. serpentine), and 30% of proton removal iseffected by electrochemical methods.

An aqueous solution comprising divalent cations (e.g., alkaline earthmetal cations such as Ca²⁺ and Mg²⁺) may be contacted with a source ofCO2 at any time before, during, or after the divalent-cation containingsolution is subjected to precipitation conditions (i.e., conditionsallowing for precipitation of one or more materials based on, forexample, pH). Accordingly, in some embodiments, an aqueous solution ofdivalent cations is contacted with a source of CO2 prior to subjectingthe aqueous solution to precipitation conditions that favor formation ofcarbonate and/or bicarbonate compounds. In some embodiments, an aqueoussolution of divalent cations is contacted with a source of CO2 while theaqueous solution is being subjected to precipitation conditions thatfavor formation of carbonate and/or bicarbonate compounds. In someembodiments, an aqueous solution of divalent cations is contacted with asource of a CO2 prior to and while subjecting the aqueous solution toprecipitation conditions that favor formation carbonate and/orbicarbonate compounds. In some embodiments, an aqueous solution ofdivalent cations is contacted with a source of CO2 after subjecting theaqueous solution to precipitation conditions that favor formation ofcarbonate and/or bicarbonate compounds. In some embodiments, an aqueoussolution of divalent cations is contacted with a source of CO2 before,while, and after subjecting the aqueous solution to precipitationconditions that favor formation of carbonate and/or bicarbonatecompounds. In some embodiments, a divalent cation-containing aqueoussolution may be cycled more than once, wherein a first cycle ofprecipitation removes primarily calcium carbonate and magnesiumcarbonate minerals and leaves an alkaline solution to which additionaldivalent cations may be added. Carbon dioxide, when contacted with therecycled solution of divalent cations, allows for the precipitation ofmore carbonate and/or bicarbonate compounds. It will be appreciatedthat, in these embodiments, the aqueous solution following the firstcycle of precipitation may be contacted with the CO2 source before,during, and/or after divalent cations have been added. In someembodiments, an aqueous solution having no divalent cations or a lowconcentration of divalent cations is contacted with CO2. In theseembodiments, the water may be recycled or newly introduced. As such, theorder of addition of CO2 and waste sources of metal oxides may vary. Forexample, a waste source of metal oxides such as fly ash, cement kilndust, or slag, each of which provides divalent cations, proton-removingagents, or both, may be added to, for example, brine, seawater, orfreshwater, followed by the addition of CO2. In another example, CO2 maybe added to, for example, brine, seawater, or freshwater, followed bythe addition of fly ash, cement kiln dust, or slag.

A divalent cation-containing aqueous solution may be contacted with aCO2 source using any convenient protocol. Where the CO2 is a gas,contact protocols of interest include, but are not limited to directcontacting protocols (e.g., bubbling the CO2 gas through the aqueoussolution), concurrent contacting means (i.e., contact betweenunidirectional flowing gaseous and liquid phase streams), countercurrentmeans (i.e., contact between oppositely flowing gaseous and liquid phasestreams), and the like. As such, contact may be accomplished through useof infusers, bubblers, fluidic Venturi reactors, spargers, gas filters,sprays, trays, or packed column reactors, and the like, as may beconvenient. In some embodiments, gas-liquid contact is accomplished byforming a liquid sheet of solution with a flat jet nozzle, wherein theCO2 gas and the liquid sheet move in countercurrent, co-current, orcrosscurrent directions, or in any other suitable manner. See, forexample, U.S. patent application Ser. No. 61/158,992, filed 10 Mar.2009, which is hereby incorporated by reference in its entirety. In someembodiments, gas-liquid contact is accomplished by contacting liquiddroplets of solution having an average diameter of 500 micrometers orless, such as 100 micrometers or less, with a CO2 gas source. In someembodiments, a catalyst is used to accelerate the dissolution of carbondioxide into solution by accelerating the reaction toward equilibrium;the catalyst may be an inorganic substance such as zinc dichloride orcadmium, or an organic substance such as an enzyme (e.g., carbonicanhydrase).

In methods of the invention, a volume of CO2 charged water produced asdescribed above is subjected to carbonate compound precipitationconditions sufficient to produce a carbonate-containing precipitationmaterial and a supernatant (i.e., the part of the precipitation reactionmixture that is left over after precipitation of the precipitationmaterial). Any convenient precipitation conditions may be employed,which conditions result in production of a carbonate-containingprecipitation material from the CO2-charged precipitation reactionmixture. Precipitation conditions include those that modulate thephysical environment of the CO2 charged precipitation reaction mixtureto produce the desired precipitation material. For example, thetemperature of the CO2-charged precipitation reaction mixture may beraised to a point at which an amount suitable for precipitation of thedesired carbonate-containing precipitation material occurs. In suchembodiments, the temperature of the CO2 charged precipitation reactionmixture may be raised to a value from 5° C. to 70° C., such as from 20°C. to 50° C., and including from 25° C. to 45° C. While a given set ofprecipitation conditions may have a temperature ranging from 0° C. to100° C., the temperature may be raised in certain embodiments to producethe desired precipitation material. In certain embodiments, thetemperature of the precipitation reaction mixture is raised using energygenerated from low or zero carbon dioxide emission sources (e.g., solarenergy source, wind energy source, hydroelectric energy source, wasteheat from the flue gases of the carbon emitter, etc). In someembodiments, the temperature of the precipitation reaction mixture maybe raised utilizing heat from flue gases from coal or other fuelcombustion. The pH of the CO2-charged precipitation reaction mixture mayalso be raised to an amount suitable for precipitation of the desiredcarbonate-containing precipitation material. In such embodiments, the pHof the CO2-charged precipitation reaction mixture is raised to alkalinelevels for precipitation, wherein carbonate is favored over bicarbonate.The pH may be raised to pH 9 or higher, such as pH 10 or higher,including pH 11 or higher. For example, when fly ash is used to raisethe pH of the precipitation reaction mixture or precursor of theprecipitation reaction mixture, the pH may be about pH 12.5 or higher.

Accordingly, a set of precipitation conditions to produce a desiredprecipitation material from a precipitation reaction mixture mayinclude, as above, the temperature and pH, as well as, in someinstances, the concentrations of additives and ionic species in thewater. Precipitation conditions may also include factors such as mixingrate, forms of agitation such as ultrasonics, and the presence of seedcrystals, catalysts, membranes, or substrates. In some embodiments,precipitation conditions include supersaturated conditions, temperature,pH, and/or concentration gradients, or cycling or changing any of theseparameters. The protocols employed to prepare carbonate-containingprecipitation material according to the invention (from start [e.g., flyash slaking] to finish [e.g., drying precipitation material or formingprecipitation material into aggregate]) may be batch, semi-batch, orcontinuous protocols. It will be appreciated that precipitationconditions may be different to produce a given precipitation material ina continuous flow system compared to a semi-batch or batch system.

Carbonate-containing precipitation material, following production from aprecipitation reaction mixture, is separated from the reaction mixtureto produce separated precipitation material (e.g., wet cake) and asupernatant as illustrated in FIG. 1. The precipitation material may bestored in the supernatant for a period of time following precipitationand prior to separation (e.g., by drying). For example, theprecipitation material may be stored in the supernatant for a period oftime ranging from 1 to 1000 days or longer, such as 1 to 10 days orlonger, at a temperature ranging from 1° C. to 40° C., such as 20° C. to25° C. Separation of the precipitation material from the precipitationreaction mixture is achieved using any of a number of convenientapproaches, including draining (e.g., gravitational sedimentation of theprecipitation material followed by draining), decanting, filtering(e.g., gravity filtration, vacuum filtration, filtration using forcedair), centrifuging, pressing, or any combination thereof. Separation ofbulk water from the precipitation material produces a wet cake ofprecipitation material, or a dewatered precipitation material. Asdetailed in U.S. 61/170,086, filed Apr. 16, 2009, which is hereinincorporate by reference, a liquid-solid separators such as Epuramat'sExtrem-Separator (“ExSep”) liquid-solid separator, Xerox PARC's spiralconcentrator, or a modification of either of Epuramat's ExSep or XeroxPARC's spiral concentrator, is useful for separation of theprecipitation material from the precipitation reaction mixture.

In some embodiments, the resultant dewatered precipitation material isthen dried to produce a product (e.g., a cement, a pozzolanic cement, anaggregate, or an non-reactive, storage-stable CO2-sequestering product).Drying may be achieved by air-drying the precipitation material. Wherethe precipitation material is air dried, air-drying may be at atemperature ranging from −70° C. to 120° C. In certain embodiments,drying is achieved by freeze-drying (i.e., lyophilization), wherein theprecipitation material is frozen, the surrounding pressure is reduced,and enough heat is added to allow the frozen water in the precipitationmaterial to sublime directly into gas. In yet another embodiment, theprecipitation material is spray-dried to dry the precipitation material,wherein the liquid containing the precipitation material is dried byfeeding it through a hot gas (such as the gaseous waste stream from thepower plant), and wherein the liquid feed is pumped through an atomizerinto a main drying chamber and a hot gas is passed as a co-current orcounter-current to the atomizer direction. Depending on the particulardrying protocol of the system, the drying station (described in moredetail below) may include a filtration element, freeze-drying structure,spray-drying structure, etc. In certain embodiments, waste heat from apower plant or similar operation may be used to perform the drying stepwhen appropriate. For example, in some embodiments, an aggregate isproduced by the use of elevated temperature (e.g., from power plantwaste heat), pressure, or a combination thereof.

Following separation of the precipitation material from the supernatant,the separated precipitation material may be further processed asdesired; however, the precipitation material may simply be transportedto a location for long-term storage, effectively sequestering CO2. Forexample, the carbonate-containing precipitation material may betransported and placed at long-term storage site, for example, aboveground (as a storage-stable CO2-sequestering material), below ground, inthe deep ocean, etc.

The resultant supernatant of the precipitation process, or a slurry ofprecipitation material may also be processed as desired. For example,the supernatant or slurry may be returned to the source of the divalentcation-containing aqueous solution (e.g., ocean) or to another location.In some embodiments, the supernatant may be contacted with a source ofCO2, as described above, to sequester additional CO2. For example, inembodiments in which the supernatant is to be returned to the ocean, thesupernatant may be contacted with a gaseous waste source of CO2 in amanner sufficient to increase the concentration of carbonate ion presentin the supernatant. As described above, contact may be conducted usingany convenient protocol. In some embodiments, the supernatant has analkaline pH, and contact with the CO2 source is carried out in a mannersufficient to reduce the pH to a range between pH 5 and 9, pH 6 and 8.5,or pH 7.5 to 8.2.

The methods of the invention may be carried out at land (e.g., at alocation where a suitable divalent cation-containing source is present,or is easily and economically transported in), at sea, in the ocean, oranother body comprising divalent cations, bit that body naturallyoccurring or manmade. In some embodiments, a system is employed toperform the above methods, where such systems include those describedbelow in greater detail.

In some embodiments of the invention, fly ash is used as the sole orprimary source of divalent cations and/or proton-removing agents forprecipitation of carbonate-containing precipitation material. In suchembodiments, fly ash may be slaked with water (e.g., freshwater,seawater, brine) to produce a slaked fly ash mixture, wherein the pH ofthe slaked fly ash mixture may be pH 7-14, pH 8-14, pH 9-14, pH 10-14,pH 11-14, pH 12-14, or pH 13-14. In such slaked fly ash mixtures, theconcentration of fly ash in water may be between 1 and 10 g/L, 10 and 20g/L, 20 and 30 g/L, 30 and 40 g/L, 40 and 80 g/L, 80 and 160 g/L, 160and 320 g/L, 320 and 640 g/L, or 640 and 1280 g/L, and the slakingtemperature may be room temperature (about 70° F.) to about 220° F.,70-100° F., 100-220° F., 120-220° F., 140-220° F., 160-200° F., or160-185° F. To optimize the extraction and conversion of CaO to Ca(OH)2,high shear mixing, wet milling, and/or sonication may be used to breakopen spheres of fly ash to access trapped CaO. High shear mixing, wetmilling, and/or sonication, in addition to providing access to CaOtrapped in the fly ash matrix (e.g., SiO2 matrix), provides for strongercements, pozzolanic cements, and related end products. After high shearmixing and/or wet milling, the slaked fly ash mixture is contacted witha source of carbon dioxide (with or without dilution of the fly ashmixture) such as flue gas from a coal-fired power plant or exhaust froma cement kiln. Any of a number of the gas-liquid contacting protocolsdescribed above may be utilized. Gas-liquid contact is continued untilthe pH of the precipitation reaction mixture is constant, after whichthe precipitation reaction mixture is allowed to stir overnight. Therate at which the pH drops may be controlled by addition of supplementalfly ash during gas-liquid contact. In addition, supplemental fly ash maybe added after sparging to raise the pH back to basic levels forprecipitation of a portion or all of the precipitation material. In anycase, precipitation material may be formed upon removing protons fromcertain species (e.g., carbonic acid, bicarbonate, hydronium) in theprecipitation reaction mixture. A precipitation material comprisingcarbonates and siliceous compounds may then be separated and,optionally, further processed.

As above, in some embodiments of the invention, fly ash is used as thesole or primary source of divalent cations and/or proton-removing agentsfor precipitation of carbonate-containing precipitation material. Insuch embodiments, fly ash may slaked with water (e.g., freshwater,seawater, brine) to produce a slaked fly ash mixture, wherein the pH ofthe slaked fly ash mixture may be pH 7-14, pH 8-14, pH 9-14, pH 10-14,pH 11-14, pH 12-14, or pH 13-14. In such slaked fly ash mixtures, theconcentration of fly ash in water may be between 1 and 10 g/L, 10 and 20g/L, 20 and 30 g/L, 30 and 40 g/L, 40 and 80 g/L, 80 and 160 g/L, 160and 320 g/L, 320 and 640 g/L, or 640 and 1280 g/L, and the slakingtemperature may be room temperature (about 70° F.) to about 220° F.,70-100° F., 100-220° F., 120-220° F., 140-220° F., 160-220° F., 160-200°F., or 160-185° F. As above, extraction and conversion of CaO to Ca(OH)2may be optimized with high shear mixing and/or wet milling; however,after any additional processing, the fly ash may be separated from theslaked fly ash mixture to produce a fly ash sludge, which may be driedand used as a pozzolan (as below), and a supernatant comprising divalentcations and proton-removing agents for precipitation ofcarbonate-containing precipitation material. The supernatant may then becontacted with a source of carbon dioxide (with or without dilution ofthe fly ash mixture) such as flue gas from a coal-fired power plant orexhaust from a cement kiln. Gas-liquid contact is continued until the pHis constant, after which the precipitation reaction mixture is allowedto stir overnight. The rate at which the pH drops may be controlled byaddition of supplemental fly ash during gas-liquid contact. In addition,supplemental fly ash may be added after gas-liquid contact to raise thepH back to basic levels for precipitation of a portion or all of theprecipitation material. In any case, precipitation material may beformed upon removing protons from certain species (e.g., carbonic acid,bicarbonate, hydronium) in the precipitation reaction mixture. Aprecipitation material comprising carbonates may then be separated and,optionally, further processed. For example, the carbonate-containingprecipitation material comprising little or no siliceous material may bedried and used in end products. The carbonate-comprising precipitationmaterial may instead be recombined with the separated fly ash sludge,wherein the precipitation material and the fly ash sludge are mixed wet,dry, or in a combination thereof, to produce a siliceous compositioncomprising carbonates. Such a material may have pozzolanic propertiesderived from the addition of wet (i.e., fly ash sludge) or dry (i.e.,dried fly ash sludge) fly ash-based pozzolan.

In some embodiments of the invention, fly ash is used in combinationwith other sources of divalent cations and/or proton-removing agents forprecipitation of carbonate-containing precipitation material. In suchembodiments, fly ash may be slaked with water (e.g., freshwater,seawater, brine) to produce a slaked fly ash mixture. Supplementalproton-removing agents may then be added to the slaked fly ash mixtureproducing a high-pH slaked fly ash mixture, wherein the pH of thehigh-pH slaked fly ash mixture may be pH 7-14, pH 8-14, pH 9-14, pH10-14, pH 11-14, pH 12-14, or pH 13-14, and the fly ash may becompletely dissolved or dissolved to some variable extent. For example,75% of the fly ash may be dissolved owing to the addition ofsupplemental proton-removing agents. In such slaked fly ash mixtures,the concentration of fly ash in water may be between 1 and 10 g/L, 10and 20 g/L, 20 and 30 g/L, 30 and 40 g/L, 40 and 80 g/L, 80 and 160 g/L,160 and 320 g/L, 320 and 640 g/L, or 640 and 1280 g/L, and the slakingtemperature may be room temperature (about 70° F.) to about 220° F.,70-100° F., 100-220° F., 120-220° F., 140-220° F., 160-220° F., 160-200°F., or 160-185° F. To facilitate dissolution of any undissolved fly ash,high shear mixing and/or wet milling may be used to break open spheresof fly ash to provide for smaller fly ash particles. After high shearmixing and/or wet milling, the slaked fly ash mixture may be contactedwith a source of carbon dioxide (with or without dilution of the fly ashmixture) such as flue gas from a coal-fired power plant or exhaust froma cement kiln. Any of a number of gas-liquid contacting protocolsdescribed above may be utilized. Gas-liquid contact is continued untilthe pH is constant, after which the precipitation reaction mixture maybe allowed to stir overnight. The rate at which the pH drops may becontrolled by addition of supplemental fly ash or another supplementalproton-removing agent during gas-liquid contact. In addition,supplemental fly ash may be added after gas-liquid contact to raise thepH back to basic levels for precipitation of a portion or all of theprecipitation material. In any case, precipitation material may beformed upon removing protons from certain species (e.g., carbonic acid,bicarbonate, hydronium) in the precipitation reaction mixture. Aprecipitation material comprising carbonates and siliceous compounds maythen be separated and, optionally, further processed.

As such, provided is a method comprising contacting an aqueous solutionwith a source of metal oxides from an industrial process; charging theaqueous solution with carbon dioxide from a source of carbon dioxidefrom an industrial process; and subjecting the aqueous solution toprecipitation conditions under atmospheric pressure to produce acarbonate-containing precipitation material. In some embodiments, thesource of metal oxides and the source of carbon dioxide are from thesame industrial process. In some embodiments, contacting the aqueoussolution with the source of metal oxides occurs prior to charging theaqueous solution with a source of carbon dioxide. In some embodiments,contacting the aqueous solution with the source of metal oxides occursat the same time as charging the aqueous solution with a source ofcarbon dioxide. In some embodiments, contacting the aqueous solutionwith the source of metal oxides, charging the aqueous solution with asource of carbon dioxide, and subjecting the aqueous solution toprecipitation conditions occurs at the same time. In some embodiments,the source of metal oxides and the source of carbon dioxide are sourcedfrom the same waste stream. In some embodiments, the waste stream isflue gas from a coal-fired power plant. In some embodiments, thecoal-fired power plant is a brown coal-fired power plant. In someembodiments, the waste stream is kiln exhaust from a cement plant. Insome embodiments, the source of metal oxides is fly ash. In someembodiments, the source of metal oxides is cement kiln dust. In someembodiments, the waste stream further comprises SOx, NOx, mercury, orany combination thereof. In some embodiments, the source of metal oxidesfurther provides divalent cations for producing the precipitationmaterial. In some embodiments, the source of metal oxides and theaqueous solution both comprise divalent cations for producing theprecipitation material. In some embodiments, the source of metal oxidesis fly ash or cement kiln dust. In some embodiments, the aqueoussolution comprises brine, seawater, or freshwater. In some embodiments,the divalent cations comprises Ca²⁺, Mg²⁺, or a combination thereof. Insome embodiments, the source of metal oxides provides proton-removingagents for producing the precipitation material. In some embodiments,the source of metal oxides provides proton-removing agents uponhydration of CaO, MgO, or a combination thereof in the aqueous solution.In some embodiments, the source of metal oxides further provides silica.In some embodiments, the source of metal oxides further providesalumina. In some embodiments, the source of metal oxides furtherprovides ferric oxide. In some embodiments, red or brown mud frombauxite processing also provides proton-removing agents. In someembodiments, electrochemical methods effecting proton removal alsoprovide for producing precipitation material.

In some embodiments, the method further comprises separating theprecipitation material from the aqueous solution from which theprecipitation material was produced. In some embodiments, theprecipitation material comprises CaCO3. In some embodiments, CaCO3comprises calcite, aragonite, vaterite, or a combination thereof. Insome embodiments, the precipitation material further comprises MgCO3. Insome embodiments, the CaCO3 comprises aragonite and the MgCO3 comprisesnesquehonite. In some embodiments, the method further comprisesprocessing the precipitation material to form a building material. Insome embodiments, the building material is a hydraulic cement. In someembodiments, the building material is a pozzolanic cement. In someembodiments, the building material is aggregate.

Also provided is a method comprising contacting an aqueous solution witha waste stream comprising carbon dioxide and a source comprising metaloxides and subjecting the aqueous solution to precipitation conditionsto produce a carbonate-containing precipitation material. In someembodiments, the waste stream is flue gas from a coal-fired power plant.In some embodiments, the coal-fired power plant is a brown coal-firedpower plant. In some embodiments, the source of metal oxides is fly ash.In some embodiments, the waste stream is kiln exhaust from a cementplant. In some embodiments, the source of metal oxides is cement kilndust. In some embodiments, the waste stream further comprises SOx, NOx,mercury, or any combination thereof. In some embodiments, divalentcations for producing the precipitation material are provided by thesource of metal oxides, the aqueous solution, or a combination thereof.In some embodiments, the aqueous solution comprises brine, seawater, orfreshwater. In some embodiments, the divalent cations comprise Ca²⁺,Mg²⁺, or a combination thereof. In some embodiments, the source of metaloxides further provides proton-removing agents for producing theprecipitation material. In some embodiments, the source of metal oxidesprovides proton-removing agents upon hydration of CaO, MgO, orcombinations thereof in the aqueous solution. In some embodiments, thesource of metal oxides further provides silica. In some embodiments, thesource of metal oxides further provides alumina. In some embodiments,the source of metal oxides further provides ferric oxide. In someembodiments, red or brown mud from bauxite processing also providesproton-removing agents. In some embodiments, electrochemical methodseffecting proton removal also provide for producing precipitationmaterial. In some embodiments, the precipitation material comprisesCaCO3. In some embodiments, CaCO3 comprises calcite, aragonite,vaterite, or a combination thereof. In some embodiments, the methodfurther comprises separating the precipitation material from the aqueoussolution from which the precipitation material was produced. In someembodiments, the method further comprises processing the precipitationmaterial to form a building material. In some embodiments, the buildingmaterial is a hydraulic cement. In some embodiments, the buildingmaterial is a pozzolanic cement. In some embodiments, the buildingmaterial is aggregate.

Compositions and Other Products

The invention provides methods and systems for utilizing waste sourcesof metal oxides to produce carbonate-containing compositions from CO2,wherein the CO2 may be from a variety of different sources (e.g., anindustrial waste by-product such as a gaseous waste stream produced by apower plant during the combustion of carbon-based fuel). As such, theinvention provides for removing or separating CO2 from a gaseous wastesource of CO2, and fixing the CO2 into a non-gaseous, storage-stableform (e.g., materials for the construction of structures such asbuildings and infrastructure, as well as the structures themselves) suchthat the CO2 cannot escape into the atmosphere. Furthermore, theinvention provides for an effective method for sequestering CO2 as wellas long-term storage of that CO2 in useable products.

Precipitation material in a storage-stable form (which may simply bedried precipitation material) may be stored above ground under exposedconditions (i.e., open to the atmosphere) without significant, if any,degradation for extended durations, e.g., 1 year or longer, 5 years orlonger, 10 years or longer, 25 years or longer, 50 years or longer, 100years or longer, 250 years or longer, 1000 years or longer, 10,000 yearsor longer, 1,000,000 years or longer, or even 100,000,000 years orlonger. As the storage-stable form of the precipitation materialundergoes little if any degradation while stored above ground undernormal rain water pH, the amount of degradation if any as measured interms of CO2 gas release from the product will not exceed 5%/year, andin certain embodiments will not exceed 1%/year. The abovegroundstorage-stable forms of the precipitation material are stable under avariety of different environment conditions, e.g., from temperaturesranging from −100° C. to 600° C. and humidity ranging from 0 to 100%where the conditions may be calm, windy or stormy. In some embodiments,the precipitation material produced by methods of the invention isemployed as a building material (e.g., a construction material for sometype of man-made structure such as buildings, roads, bridges, dams, andthe like), such that CO2 is effectively sequestered in the builtenvironment. Any man made structure, such as foundations, parkingstructures, houses, office buildings, commercial offices, governmentalbuildings, infrastructures (e.g., pavements; roads; bridges; overpasses;walls; footings for gates, fences and poles; and the like) is considereda part of the built environment. Mortars of the invention find use inbinding construction blocks (e.g., bricks) together and filling gapsbetween construction blocks. Mortars can also be used to fix existingstructure (e.g., to replace sections where the original mortar hasbecome compromised or eroded), among other uses.

In certain embodiments, the carbonate-containing composition is employedas a component of a hydraulic cement, which sets and hardens aftercombining with water. Setting and hardening of the product produced bycombining the precipitation material with cement and water results fromthe production of hydrates that are formed from the cement upon reactionwith water, wherein the hydrates are essentially insoluble in water.Such carbonate compound hydraulic cements, methods for theirmanufacture, and use are described in U.S. patent application Ser. No.12/126,776 titled “Hydraulic Cements Comprising Carbonate CompoundsCompositions” and filed on May 23, 2008; the disclosure of whichapplication is herein incorporated by reference.

Adjusting major ion ratios during precipitation may influence the natureof the precipitation material. Major ion ratios have considerableinfluence on polymorph formation. For example, as the magnesium:calciumratio in the water increases, aragonite becomes the major polymorph ofcalcium carbonate in the precipitation material over low-magnesiumcalcite. At low magnesium:calcium ratios, low-magnesium calcite becomesthe major polymorph. In some embodiments, where Ca²⁺ and Mg²⁺ are bothpresent, the ratio of Ca²⁺ to Mg²⁺ (i.e., Ca²⁺:Mg²⁺) in theprecipitation material is 1:1 to 1:2.5; 1:2.5 to 1:5; 1:5 to 1:10; 1:10to 1:25; 1:25 to 1:50; 1:50 to 1:100; 1:100 to 1:150; 1:150 to 1:200;1:200 to 1:250; 1:250 to 1:500; or 1:500 to 1:1000. In some embodiments,the ratio of Mg²⁺ to Ca²⁺ (i.e., Mg²⁺:Ca²⁺) in the precipitationmaterial is 1:1 to 1:2.5; 1:2.5 to 1:5; 1:5 to 1:10; 1:10 to 1:25; 1:25to 1:50; 1:50 to 1:100; 1:100 to 1:150; 1:150 to 1:200; 1:200 to 1:250;1:250 to 1:500; or 1:500 to 1:1000.

Precipitation rate may also have a large effect on compound phaseformation, with the most rapid precipitation rate achieved by seedingthe solution with a desired phase. Without seeding, rapid precipitationmay be achieved by rapidly increasing the pH of the precipitationreaction mixture, which results in more amorphous constituents. The morerapid the reaction rate, the more silica is incorporated with thecarbonate-containing precipitation material, provided silica is presentin the precipitation reaction mixture. Furthermore, the higher the pH,the more rapid the precipitation, which results in a more amorphousprecipitation material.

In addition to magnesium- and calcium-containing products of theprecipitation reaction, compounds and materials comprising silicon,aluminum, iron, and others may also be prepared with methods and systemsof the invention. Precipitation of such compounds may be desired toalter the reactivity of cements comprising the precipitated materialresulting from the process, or to change the properties of cured cementsand concretes made from them. In some embodiments, combustion ash suchas fly ash is added to the precipitation reaction mixture as one sourceof these components, to produce carbonate-containing precipitationmaterial which contains one or more components, such as amorphoussilica, amorphous alumino-silicates, crystalline silica, calciumsilicates, calcium alumina silicates, etc. In some embodiments, theprecipitation material comprises carbonates (e.g., calcium carbonate,magnesium carbonate) and silica in a carbonate:silica ratio of 1:1 to1:1.5; 1:1.5 to 1:2; 1:2 to 1:2.5; 1:2.5 to 1:3; 1:3 to 1:3.5; 1:3.5 to1:4; 1:4 to 1:4.5; 1:4.5 to 1:5; 1:5 to 1:7.5; 1:7.5 to 1:10; 1:10 to1:15; or 1:15 to 1:20. In some embodiments, the precipitation materialcomprises silica and carbonates (e.g., calcium carbonate, magnesiumcarbonate) in a silica:carbonate ratio of 1:1 to 1:1.5; 1:1.5 to 1:2;1:2 to 1:2.5; 1:2.5 to 1:3; 1:3 to 1:3.5; 1:3.5 to 1:4; 1:4 to 1:4.5;1:4.5 to 1:5; 1:5 to 1:7.5; 1:7.5 to 1:10; 1:10 to 1:15; or 1:15 to1:20.

Precipitation material comprising silica and aluminosilicates may bereadily employed in the cement and concrete industry as pozzolaniccement by virtue of the presence of the finely divided siliceous and/oralumino-siliceous material. The siliceous and/or aluminosiliceousprecipitation material may be used with Portland cement to produce ablended cement or as a direct mineral admixture in a concrete mixture.In some embodiments, pozzolanic material, which may be precipitationmaterial alone or mixed with additional fly ash and/or wet or dried flyash sludge, comprises calcium and magnesium in a ratio (as above) thatperfects setting time, stiffening, and long-term stability of resultanthydration products. Crystallinity of carbonates, concentration ofchlorides, alkalis, etc. in the precipitation material may also becontrolled to better interact with Portland cement. In some embodiments,siliceous precipitation material comprises silica in which 10-20%,20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, 90-95%, 95-98%,98-99%, 99-99.9% of the silica has a particle size less than 45 microns(e.g., in the biggest dimension). In some embodiments, siliceousprecipitation material comprises aluminosilica in which 10-20%, 20-30%,30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, 90-95%, 95-98%, 98-99%,99-99.9% of the aluminosilica has a particle size less than 45 microns.In some embodiments, siliceous precipitation material comprises amixture of silica and aluminosilica in which 10-20%, 20-30%, 30-40%,40-50%, 50-60%, 60-70%, 70-80%, 80-90%, 90-95%, 95-98%, 98-99%, 99-99.9%of the mixture has a particle size less than 45 microns (e.g., in thebiggest dimension).

As such, provided is a siliceous composition comprising a syntheticcalcium carbonate, wherein the calcium carbonate is present in at leasttwo forms selected from calcite, aragonite, and vaterite. In someembodiments, the at least two forms of calcium carbonate are calcite andaragonite. In some embodiments, calcite and aragonite are present in aratio of 20:1. In some embodiments, calcium carbonate and silica arepresent in a ratio of at least 1:2, carbonate to silica. In someembodiments, 75% of the silica is amorphous silica less than 45 micronsin particle size. In some embodiments, silica particles are wholly orpartially encapsulated by the synthetic calcium carbonate or syntheticmagnesium carbonate.

Also provided is a siliceous composition comprising synthetic calciumcarbonate and synthetic magnesium carbonate, wherein the calciumcarbonate is present in at least a form selected from calcite,aragonite, and vaterite, and wherein magnesium carbonate is present inat least a form selected from nesquehonite, magnesite, andhydromagnesite. In some embodiments, the calcium carbonate is present asaragonite and the magnesium carbonate is present as nesquehonite. Insome embodiments, silica is 20% or less of the siliceous composition. Insome embodiments, silica is 10% or less of the siliceous composition. Insome embodiments, silica particles are wholly or partially encapsulatedby the synthetic calcium carbonate or synthetic magnesium carbonate.

In some embodiments, an aggregate is produced from the resultantprecipitation material. In such embodiments, where the drying processproduces particles of the desired size, little if any additionalprocessing is required to produce the aggregate. In yet otherembodiments, further processing of the precipitation material isperformed in order to produce the desired aggregate. For example, theprecipitation material may be combined with fresh water in a mannersufficient to cause the precipitate to form a solid product, where themetastable carbonate compounds present in the precipitate have convertedto a form that is stable in fresh water. By controlling the watercontent of the wet material, the porosity, and eventual strength anddensity of the final aggregate may be controlled. Typically a wet cakewill be 40-60 volume % water. For denser aggregates, the wet cake willbe <50% water, for less dense cakes, the wet cake will be >50% water.After hardening, the resultant solid product may then be mechanicallyprocessed, e.g., crushed or otherwise broken up and sorted to produceaggregate of the desired characteristics, e.g., size, particular shape,etc. In these processes the setting and mechanical processing steps maybe performed in a substantially continuous fashion or at separate times.In certain embodiments, large volumes of precipitate may be stored inthe open environment where the precipitate is exposed to the atmosphere.For the setting step, the precipitate may be irrigated in a convenientfashion with fresh water, or allowed to be rained on naturally or orderto produce the set product. The set product may then be mechanicallyprocessed as described above. Following production of the precipitate,the precipitate is processed to produce the desired aggregate. In someembodiment the precipitate may be left outdoors, where rainwater can beused as the freshwater source, to cause the meteoric water stabilizationreaction to occur, hardening the precipitate to form aggregate.

In an example of one embodiment of the invention, the precipitate ismechanically spread in a uniform manner using a belt conveyor andhighway grader onto a compacted earth surface to a depth of interest,e.g., up to twelve inches, such as 1 to 12 inches, including 6 to 12inches. The spread material is then irrigated with fresh water at aconvenient rate, e.g., of one/half gallon of water per cubic foot ofprecipitate. The material is then compacted using multiple passes with asteel roller, such as those used in compacting asphalt. The surface isre-irrigated on a weekly basis until the material exhibits the desiredchemical and mechanical properties, at which point the material ismechanically processed into aggregate by crushing.

In an example of an additional embodiment of the invention, thecarbonate-containing precipitation material, once separated from theprecipitation reaction mixture, is washed with fresh water, then placedinto a filter press to produce a filter cake with 30-60% solids. Thisfilter cake is then mechanically pressed in a mold, using any convenientmeans, e.g., a hydraulic press, at adequate pressures, e.g., rangingfrom 5 to 5000 psi, such as 1000 to 5000 psi, to produce a formed solid,e.g., a rectangular brick. These resultant solids are then cured, e.g.,by placing outside and storing, by placing in a chamber wherein they aresubjected to high levels of humidity and heat, etc. These resultantcured solids are then used as building materials themselves or crushedto produce aggregate. Methods of producing such aggregate are furtherdescribed in U.S. patent application Ser. No. 12/475,378, filed 29 May2009, the disclosure of which is herein incorporated by reference.

In processes involving the use of temperature and pressure, thedewatered water precipitate cake is generally first dried. The cake isthen exposed to a combination of rewatering, and elevated temperatureand/or pressure for a certain time. The combination of the amount ofwater added back, the temperature, the pressure, and the time ofexposure, as well as the thickness of the cake, can be varied accordingto composition of the starting material and the desired results. Anumber of different ways of exposing the material to temperature andpressure are described herein; it will be appreciated that anyconvenient method may be used. An exemplary drying protocol is exposureto 40° C. for 24-48 hours, but greater or lesser temperatures and timesmay be used as convenient, e.g., 20-60° C. for 3-96 hours or evenlonger. Water is added back to the desired percentage, e.g., to 1%-50%,e.g., 1% to 10%, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% w/w, such as5% w/w, or 4-6% w/w, or 3-7% w/w. In some cases an exact percentage ofwater added back is not important, as in materials that are storedoutdoors and exposed to meteoric precipitation. Thickness and size ofthe cake may be adjusted as desired; the thickness can vary in someembodiment from 0.05 inch to 5 inches, e.g. 0.1-2 inches, or 0.3-1 inch.In some embodiments the cake may be 0.5 inch to 6 feet or even thicker.The cake is then exposed to elevated temperature and/or pressure for agiven time, by any convenient method, for example, in a platen pressusing heated platens. The heat to elevate the temperature, e.g., for theplatens, may be provided, e.g., by heat from an industrial waste gasstream such as a flue gas stream. The temperature may be any suitabletemperature; in general, for a thicker cake a higher temperature isdesired; examples of temperature ranges are 40-150° C., e.g., 60-120°C., such as 70-110° C., or 80-100° C. Similarly, the pressure may be anysuitable pressure to produce the desired results; exemplary pressuresinclude 1000-100,000 pounds per square inch (psi), including 2000-50,000psi, or 2000-25,000 psi, or 2000-20,000 psi, or 3000-5000 psi. Finally,the time that the cake is pressed may be any suitable time, e.g., 1-100seconds, or 1-100 minute, or 1-50 minutes, or 2-25 minutes, or 1-10,000days. The resultant hard tablet may optionally then cured, e.g., byplacing outside and storing, by placing in a chamber wherein they aresubjected to high levels of humidity and heat, etc. These hard tablets,optionally cured, are then used as building materials themselves orcrushed to produce aggregate.

One method of providing temperature and pressure is to stack dewateredand dried slabs. For example, in such a method a dewatered precipitatemay be dried, e.g., with flue gas, in a slab, e.g., 1 inch to 10 feetthick, or 1 foot to 10 feet thick. Pressure is supplied by placing slabson top of each other; greater pressure is achieved by greaterthicknesses of slab layers, e.g., 10-1000 feet or even greater, such as100-5000 feet. At an appropriate time, which may be days, weeks, months,or even years, depending on the desired result, citified slabs from agiven level of the layers, e.g., from the bottom, is removed, e.g., byquarrying, and treated as desired to produce an aggregate or other rockmaterial.

Another method of providing temperature and pressure is the use of apress, as described more fully in U.S. patent application Ser. No.12/475,378, filed 29 May 2009. A suitable press, e.g., a platen press,may be used to provide pressure at the desired temperature (using heatsupplied, e.g., by a flue gas or by other steps of the process toproduce a precipitate, e.g., from an electrochemical process) for adesired time. A set of rollers may be used in similar fashion.

Another way to expose the cake to elevated temperature and pressure isby means of an extruder e.g., a screw-type extruder, also describedfurther in U.S. patent application Ser. No. 12/475,378, filed 29 May2009. The barrel of the extruder can be outfitted to achieve an elevatedtemperature, e.g., by jacketing; this elevated temperature can besupplied by, e.g., flue gases or the like. Extrusion may be used as ameans of pre-heating and drying the feedstock prior to a pressingoperation. Such pressing can be performed by means of a compressionmold, via rollers, via rollers with shaped indentations (which canprovide virtually any shape of aggregate desired), between a belt whichprovides compression as it travels, or any other convenient method.Alternatively, the extruder may be used to extrude material through adie, exposing the material to pressure as it is forced through the die,and giving any desired shape. In some embodiments, the carbonate mineralprecipitate is mixed with fresh water and then placed into the feedsection of a rotating screw extruder. The extruder and/or the exit diemay be heated to further assist in the process. The turning of the screwconveys the material along its length and compresses it as the flitedepth of the screw decreases. The screw and barrel of the extruder mayfurther include vents in the barrel with decompression zones in thescrew coincident with the barrel vent openings. Particularly in the caseof a heated extruder, these vented areas allow for the release of steamfrom the conveyed mass, removing water from the material.

The screw conveyed material is then forced through a die section whichfurther compresses the material and shapes it. Typical openings in thedie can be circular, oval, square, rectangular, trapezoidal, etc.,although any shape which the final aggregate is desired in could be madeby adjusting the shape of the opening. The material exiting the die maybe cut to any convenient length by any convenient method, such as by afly knife. A typical length can be from 0.05 inches to 6 inches,although lengths outside those ranges are possible. Typical diameterscan be 0.05 inches to 1.0 inches, though diameters outside of theseranges are possible.

Use of a heated die section may further assist in the formation of theaggregate by accelerating the transition of the carbonate mineral to ahard, stable form. Heated dies may also be used in the case of bindersto harden or set the binder. Temperatures of 100° C. to 600° C. arecommonly used in the heated die section. Heat for the heated die maycome in whole or in part from the flue gas or other industrial gas usedin the process of producing the precipitate, where the flue gas is firstrouted to the die to transfer heat from the hot flue gas to the die.

In yet other embodiments, the precipitate may be employed for in situ orform-in-place structure fabrication. For example, roads, paved areas, orother structures may be fabricated from the precipitate by applying alayer of precipitate, e.g., as described above, to a substrate, e.g.,ground, roadbed, etc., and then hydrating the precipitate, e.g., byallowing it to be exposed to naturally applied water, such as in theform of rain, or by irrigation. Hydration solidifies the precipitateinto a desired in situ or form-in-place structure, e.g., road, pavedover area, etc. The process may be repeated, e.g., where thicker layersof in-situ formed structures are desired.

Systems

Aspects of the invention further include systems, e.g., processingplants or factories, for practicing the methods as described above.Systems of the invention may have any configuration that enablespractice of the particular production method of interest. In someembodiments, the system is configured to produce carbonate-containingprecipitation material in excess of 1 ton per day. In some embodiments,the system is configured to produce carbonate-containing precipitationmaterial in excess of 10 tons per day. In some embodiments, the systemis configured to produce carbonate-containing precipitation material inexcess of 100 tons per day. In some embodiments, the system isconfigured to produce carbonate-containing precipitation material inexcess of 1000 tons per day. In some embodiments, the system isconfigured to produce carbonate-containing precipitation material inexcess of 10,000 tons per day.

In certain embodiments, the systems include a source of divalentcation-containing aqueous solution such as a structure having an inputfor the aqueous solution. For example, the systems may include apipeline or analogous feed of divalent cation-containing aqueoussolution, wherein the divalent cation-containing aqueous solution isbrine, seawater, or freshwater. In some embodiments, the systemcomprises a structure having an input for water comprising no divalentcations or a low concentration of divalent cations. In some embodiments,the structure and input is configured to provide water (with divalentcations or not) sufficient to produce precipitation material in excessof 1, 10, 100, 1,000, or 10,000 tons per day.

In addition, the systems will include a precipitation reactor thatsubjects the water introduced to the precipitation reactor to carbonatecompound precipitation conditions (as described above) and producesprecipitation material and supernatant. In some embodiments, theprecipitation reactor is configured to provide water (with divalentcations or not) sufficient to produce precipitation material in excessof 1, 10, 100, 1,000, or 10,000 tons per day. The precipitation reactormay also be configured to include any of a number of different elementssuch as temperature modulation elements (e.g., configured to heat thewater to a desired temperature), chemical additive elements (e.g.,configured for introducing divalent cations, proton-removing agents,etc. into the precipitation reaction mixture), electrolysis elements(e.g., cathodes, anodes, etc.), and the like.

The system further includes a source of CO2 and a waste source of metaloxides, as well as components for combining these sources with water(optionally a divalent-cation containing aqueous solution such as brineor seawater) at some point before the precipitation reactor or in theprecipitation reactor. As such, the precipitation system may include aseparate source of CO2, for example, wherein the system is configured tobe employed in embodiments where the aqueous solution of divalentcations and/or supernatant is contacted with a carbon dioxide source atsome time during the process. This source may be any of those describedabove (e.g., a waste feed from an industrial power plant), gas contactbeing effected by, for example, a gas-liquid contactor such as thatdescribed in U.S. Provisional Patent Application 61/178,475, filed 14May 2009, which is hereby incorporated by reference in its entirety. Insome embodiments, the gas-liquid contactor is configured to contactenough CO2 to produce precipitation material in excess of 1, 10, 100,1,000, or 10,000 tons per day.

A gaseous waste stream may be provided from an industrial plant to thesite of precipitation in any convenient manner that conveys the gaseouswaste stream from the industrial plant to the precipitation plant. Insome embodiments, the gaseous waste stream is provided with a gasconveyer (e.g., a duct) that runs from a site of the industrial plant(e.g., an industrial plant flue) to one or more locations of theprecipitation site. The source of the gaseous waste stream may be adistal location relative to the site of precipitation such that thesource of the gaseous waste stream is a location that is 1 mile or more,such as 10 miles or more, including 100 miles or more, from theprecipitation location. For example, the gaseous waste stream may havebeen transported to the site of precipitation from a remote industrialplant via a CO2 gas conveyance system (e.g., a pipeline). The industrialplant generated CO2 containing gas may or may not be processed (e.g.,remove other components) before it reaches the precipitation site (i.e.,the site in which precipitation and/or production of aggregate takesplace). In yet other instances, the gaseous waste stream source isproximal to the precipitation site. For example, the precipitation siteis integrated with the gaseous waste stream source, such as a powerplant that integrates a precipitation reactor for precipitation ofprecipitation material that may be used to produce aggregate.

As indicated above, the gaseous waste stream may be one that is obtainedfrom a flue or analogous structure of an industrial plant. In theseembodiments, a line (e.g., duct) is connected to the flue so that gasleaves the flue through the line and is conveyed to the appropriatelocation(s) of a precipitation system. Depending upon the particularconfiguration of the precipitation system at the point at which thegaseous waste stream is employed, the location of the source from whichthe gaseous waste stream is obtained may vary (e.g., to provide a wastestream that has the appropriate or desired temperature). As such, incertain embodiments, where a gaseous waste stream having a temperatureranging for 0° C. to 1800° C., such as 60° C. to 700° C., is desired,the flue gas may be obtained at the exit point of the boiler or gasturbine, the kiln, or at any point of the power plant or stack, thatprovides the desired temperature. Where desired, the flue gas ismaintained at a temperature above the dew point (e.g., 125° C.) in orderto avoid condensation and related complications. If it is not possibleto maintain the temperature above the dew point, steps may be taken toreduce the adverse impact of condensation (e.g., employing ducting thatis stainless steel, fluorocarbon (such as poly(tetrafluoroethylene))lined, diluted with water, and pH controlled, etc.) so the duct does notrapidly deteriorate.

Where the saltwater source that is processed by the system to producethe carbonate compound composition is seawater, the input is in fluidcommunication with a source of sea water, e.g., such as where the inputis a pipeline or feed from ocean water to a land based system or a inletport in the hull of ship, e.g., where the system is part of a ship,e.g., in an ocean based system.

The system further includes a liquid-separator separator for separatingcarbonate-containing precipitation material from the reaction mixturefrom which it was produced. As detailed in U.S. Provisional PatentApplication 61/170,086, filed 16 Apr. 2009, which is herein incorporateby reference, liquid-solid separators such as Epuramat'sExtrem-Separator (“ExSep”) liquid-solid separator, Xerox PARC's spiralconcentrator, or a modification of either of Epuramat's ExSep or XeroxPARC's spiral concentrator, is useful for separation of theprecipitation material from the precipitation reaction mixture. Incertain embodiments, the separator is a drying station for drying theprecipitated carbonate mineral composition produced by the carbonatemineral precipitation station. Depending on the particular dryingprotocol of the system, the drying station may include a filtrationelement, freeze drying structure, spray drying structure, etc., asdescribed more fully below.

In certain embodiments, the system will further include a station forpreparing a building material, such as cement or aggregate, from theprecipitate. See e.g., U.S. patent application Ser. No. 12/126,776titled “Hydraulic Cements Comprising Carbonate Compounds Compositions”and filed on May 23, 2008 and U.S. Provisional Patent Application Ser.No. 61/056,972 titled “CO2 Sequestering Aggregate, and Methods of Makingand Using the Same,” filed on May 23, 2008, the disclosures of whichapplications are herein incorporated by reference.

As indicated above, the system may be present on land or sea. Forexample, the system may be land-based system that is in a coastalregion, e.g., close to a source of seawater, or even an interiorlocation, where water is piped into the system from a salt-water source,e.g., ocean. Alternatively, the system bay a water based system, i.e., asystem that is present on or in water. Such a system may be present on aboat, ocean based platform etc., as desired.

FIG. 1 depicts a typical power plant process for burning coal andremoving wastes such as ash and sulfur. Coal 500 is burned in steamboiler 501, which produces steam to power a turbine generator andproduce electricity. The burning of the coal produces flue gas 502,which contains CO2, SOx, NOx, Hg, etc. as well as fly ash. The burningof the coal also produces bottom ash 510, which may be sent to alandfill or used as a low-value aggregate. The flue gas 502 is runthrough a separation device 520, generally an electrostaticprecipitator, which results in removal of fly ash 530 from the flue gas502. Depending on the manner of combustion and the type of coal, fly ash530 may find beneficial use in concrete, but is more generally landfilled.

A fan 540 directs the sulfur containing flue gas 521 to FGD tank 550,where it is treated by exposure to a lime slurry 553 prepared from water551 and calcined lime 552. The calcination of lime releases CO2 into theatmosphere, so for every mole of lime used one mole of CO2 is releasedin producing the lime. The lime 552 combines with SOx from the flue gas521 t in FGD tank 550 to produce gypsum (CaSO4). Thus for every moleculeof sulfur removed from the flue gas, one molecule of CO2 has beenreleased into the atmosphere from calcination of the lime.

Sulfur-free flue gas 556 is piped from FGD tank 550 to stack 560, whereit may be further treated to remove NOx, Hg, etc. before being releasedinto the atmosphere as gas 580. Note that gas 580, which is released tothe atmosphere, still contains most if not all of the CO2, which wasgenerated by burning of the coal 500.

The reaction of calcined lime slurry 553 with sulfur-containing flue gas521 in FGD tank 550 produces a gypsum slurry 554 which is moved tohydrocyclone 570 by means of pump 555. Hydrocyclone 570 removes water571 from slurry 554, producing a more concentrated gypsum slurry 579,which is sent to filter 580 for further dewatering. The water removed inhydrocyclone 570 and filter 580 is sent to reclaim water tank 572, whereexcess solids are settled out and sent to landfill 511. Wastewater 574is discharged and some reclaim water 573 is sent back to FGD tank 550.The filter cake 581, which is removed from filter 580, is sent to dryer583, where water is removed to produce dry gypsum powder 590. Gypsumpowder 590 way be sent to landfill 511, or may be used to producebuilding materials such as wallboard.

FIG. 2 represents an example of one embodiment of the invention in whichCO2, fly ash, NOx, SOx, Hg and other pollutants are utilized asreactants in a carbonate compound precipitation process to remove thesemoieties and sequester them into the built environment, e.g., via theiruse in a hydraulic cement. In this example, the fly ash and bottom ashare utilized as reactants to both lower pH and to provide beneficialco-reacting cations, such as silicon and aluminum.

Coal 600 is burned in steam boiler 601, which produces steam to power aturbine generator and produce electricity. The burning of the coalproduces flue gas 602, which contains CO2, SOx, NOx, Hg, etc. as well asfly ash. In this embodiment, the coal utilized is a high-sulfursub-bituminous coal, which is inexpensive to obtain but which produceslarger quantities of SOx and other pollutants. Flue gas 602, bottom ash610, seawater 620 and in some embodiments additional alkali source 625are charged into reactor 630, wherein a carbonate mineral precipitationprocess takes place, producing slurry 631.

Slurry 631 is pumped via pump 640 to drying system 650, which in someembodiments includes a filtration step followed by spray drying. Thewater 651 separated from the drying system 650 is discharged, along withclean gas 680, which can be released to the atmosphere. The resultantsolid or powder 660 from drying system 650 is utilized as a hydrauliccement to produce building materials, effectively sequestering the CO2,SOx, and, in some embodiments, other pollutants such as mercury and/orNOx into the built environment.

As such, provided is a system comprising a slaker adapted to slake awaste source of metal oxides, a precipitation reactor; and aliquid-solid separator, wherein the precipitation reactor is operablyconnected to both the slaker and the liquid-solid separator, and furtherwherein the system is configured to produce carbonate-containingprecipitation material in excess of 1 ton per day. In some embodiments,the system is configured to produce carbonate-containing precipitationmaterial in excess of 10 tons per day. In some embodiments, the systemis configured to produce carbonate-containing precipitation material inexcess of 100 ton per day. In some embodiments, the system is configuredto produce carbonate-containing precipitation material in excess of 1000tons per day. In some embodiments, the system is configured to producecarbonate-containing precipitation material in excess of 10,000 tons perday. In some embodiments, the slaker is selected from a slurry detentionslaker, a paste slaker, and a ball mill slaker. In some embodiments, thesystem further comprises a source of carbon dioxide. In someembodiments, the source of carbon dioxide is from a coal-fired powerplant or cement plant. In some embodiments, the system further comprisesa source of proton-removing agents. In some embodiments, the systemfurther comprises a source of divalent cations. In some embodiments, thesystem further comprising a building-materials production unitconfigured to produce a building material from solid product of theliquid-solid separator.

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the invention, and are not intended to limit the scope ofwhat the inventors regard as their invention nor are they intended torepresent that the experiments below are all or the only experimentsperformed. Efforts have been made to ensure accuracy with respect tonumbers used (e.g. amounts, temperature, etc.) but some experimentalerrors and deviations should be accounted for. Unless indicatedotherwise, parts are parts by weight, molecular weight is weight averagemolecular weight, temperature is in degrees Centigrade, and pressure isat or near atmospheric.

EXAMPLES

The following analytical instrumentation and methods of use thereof wereused to characterize materials produced in the examples below.

Coulometer: Liquid and solid carbon-containing samples were acidifiedwith 2.0 N perchloric acid (HClO4) to evolve carbon dioxide gas into acarrier gas stream, and subsequently scrubbed with 3% w/v silver nitrateat pH 3.0 to remove any evolved sulfur gasses prior to analysis by aninorganic carbon coulometer (UIC Inc, model CM5015). Samples of cement,fly ash, and seawater are heated after addition of percholoric acid witha heated block to aid digestion of the sample.

Brunauer-Emmett-Teller (“BET”) Specific Surface Area: Specific surfacearea (SSA) measurement was by surface absorption with dinitrogen (BETmethod). SSA of dry samples was measured with a Micromeritics Tristar™II 3020 Specific Surface Area and Porosity Analyzer after preparing thesample with a Flowprep™ 060 sample degas system. Briefly, samplepreparation involved degassing approximately 1.0 g of dry sample at anelevated temperature while exposed to a stream of dinitrogen gas toremove residual water vapour and other adsorbants from the samplesurfaces. The purge gas in the sample holder was subsequently evacuatedand the sample cooled before being exposed to dinitrogen gas at a seriesof increasing pressures (related to adsorption film thickness). Afterthe surface was blanketed, the dinitrogen was released from the surfaceof the particles by systematic reduction of the pressure in the sampleholder. The desorbed gas was measured and translated to a total surfacearea measurement.

Particle Size Analysis (“PSA”): Particle size analysis and distributionwere measured using static light scattering. Dry particles weresuspended in isopropyl alcohol and analyzed using a Horiba Particle SizeDistribution Analyzer (Model LA-950V2) in dual wavelength/laserconfiguration. Mie scattering theory was used to calculate thepopulation of particles as a function of size fraction, from 0.1 mm to1000 mm.

Powder X-ray Diffraction (“XRD”): Powder X-ray diffraction wasundertaken with a Rigaku Miniflex™ (Rigaku) to identify crystallinephases and estimate mass fraction of different identifiable samplephases. Dry, solid samples were hand-ground to a fine powder and loadedon sample holders. The X-ray source was a copper anode (Cu kα), poweredat 30 kV and 15 mA. The X-ray scan was run over 5-90°2θ, at a scan rateof 2°2θ per min, and a step size of 0.01°2θ per step. The X-raydiffraction profile was analyzed by Rietveld refinement using the X-raydiffraction pattern analysis software Jade™ (version 9, Materials DataInc. (MDI)).

Fourier Transform Infrared (“FT-IR”) Spectroscopy: FT-IR analyses wereperformed on a Nicolet 380 equipped with the Smart Diffuse Reflectancemodule. All samples were weighed to 3.5±0.5 mg and hand ground with 0.5g KBr and subsequently pressed and leveled before being inserted intothe FT-IR for a 5-minute nitrogen purge. Spectra were recorded in therange 400-4000 cm⁻¹.

Scanning Electron Microscopy (“SEM”): SEM was performed using an HitachiTM-1000 tungsten filament tabletop microscope using a fixed accelerationvoltage of 15 kV at a working pressure of 30-65 Pa, and a single BSEsemiconductor detector. Solid samples were fixed to the stage using acarbon-based adhesive; wet samples were vacuum dried to a graphite stageprior to analysis.

Chloride Concentration: Chloride concentrations were determined withChloride QuanTab® Test Strips (Product No. 2751340), having a testingrange between 300-6000 mg chloride per liter solution measured in100-200 ppm increments.

Example 1 Fly Ash pH Study A. Experimental

500 mL of seawater (initial pH=8.01) was continuously stirred in a glassbeaker using a magnetic stir bar. The pH and temperature of the reactionwas continuously monitored. Class F fly ash (˜10% CaO) was incrementallyadded as a powder, allowing the pH to equilibrate in between additions.

B. Results and Observations

(Amounts of fly ash listed are the cumulative totals, i.e. the totalamount added at that point in the experiment.)

After the additions of 5.00 g of fly ash the pH reached 9.00.

Fly ash (g) pH 5.00 9.00 34.14 9.50 168.89 9.76 219.47 10.94 254.1311.20 300.87 11.28

Much more fly ash was needed to raise the pH of the seawater thandistilled water. The initial rise in pH (pH 8 to pH 9) required muchless fly ash than the subsequent rises in pH of the same magnitude. ThepH remained fairly stable around 9.7 for much of the reaction. The rateof pH increase went up after ˜10. Also of note was an initial drop in pHwhen the fly ash was added. This drop in pH is quickly overcome by theeffects of the calcium hydroxide. SEM images of vacuum-dried slurry fromthe reaction indicated that some spheres of the fly ash may havepartially dissolved. The remaining spheres also seemed to be embedded ina possibly cementitious material.

C. Conclusions

In fresh (distilled) water, it was found that small amounts of class Ffly ash (<1 g/L) immediately raised the pH from 7 (neutral) to ˜11. Thesmall amount necessary to raise the pH is most likely due to theunbuffered nature of nature of distilled water. Seawater is highlybuffered by the carbonate system, and thus it took much more fly ash toraise the pH to similar levels.

Example 2 Precipitation Material Using Fly Ash as Source of DivalentCations and Proton-Removing Agents

Protocol A. Slaking

-   -   1. Fly ash (322.04 g of FAF11-001) was weighed into a 500 mL        plastic reaction vessel.    -   2. Deionized water (320.92 g) was added to the reaction vessel        resulting in a 1:1 ratio of fly ash to water.    -   3. Resultant mixture stirred until a homogeneous slurry.    -   4. Reaction vessel closed and sealed with tape.    -   5. Slurry was rotated for 24 hours.

B. Precipitation

-   -   1. Deionized water (680 ml at pH 7.13) was added to a 2 L        plastic reaction vessel equipped with a large stir bar and        stirred at 250 rpm.    -   2. Slaked slurry was slowly added with stirring, resulting in a        reaction mixture that was about 320 g fly ash per liter.    -   3. Stirring maintained until a stable pH level was reached (pH        12.40).    -   4. 15% CO2 in compressed air was added (CO2: 0.4 scfh;        compressed air: 2.1 scfh; total: 2.5 scfh) using a sparger        placed as low in the reaction mixture as possible (without        disturbing the stir bar).    -   5. Reaction vessel was covered, leaving only a small opening for        the gas tubing and pH probe.    -   6. pH monitored and recorded for over 5 hours.    -   7. After adequate CO2 was added to the reaction slurry (i.e. ˜2×        equivalents based on CaO/MgO in fly ash as measured by XRF), CO2        sparging was stopped (by removing the sparger), the reaction        vessel was sealed, and the precipitation reaction mixture was        allowed to stir overnight at 250 rpm.

Work Up 1. pH of the precipitation reaction mixture was measured at pH8.37 after stirring overnight.

-   -   2. Stirring was stopped and the precipitation reaction mixture        was filtered.    -   3. Resultant precipitation material was dried overnight at 50°        C.    -   4. Resultant supernatant was collected.

Analysis 1. Precipitation material was analyzed by SEM, XRD TGA,coulometry, and FT-IR. FIG. 3 provides SEM images of the precipitationmaterial of at 1000×, 2500×, and 6000× magnification. FIG. 4 provides anXRD of the precipitation material. FIG. 5 provides a TGA for theprecipitation material. Coulometry indicated that the precipitationmaterial 1.795% carbon.

-   -   2. Supernatant was analyzed using alkalinity and hardness.

TABLE 3 Reaction profile for Example 2. CO2 Delivered CO2 Air Time (min)pH (moles) (on/off) (on/off) 0 7.13 0.000 off off 0 12.39 0.000 off off0 12.40 0.000 off off 1 12.37 0.008 on on 2 12.33 0.015 on on 4 12.270.030 on on 5 12.22 0.038 on on 7 12.10 0.053 on on 9 11.98 0.068 on on16 11.51 0.122 on on 42 10.55 0.319 on on 51 9.93 0.387 on on 55 9.770.418 on on 115 8.66 0.873 on on 180 8.14 1.367 off off 230 7.60 1.747off off 285 7.13 2.165 off off 345 7.31 2.620 off off

Example 3 Precipitation Material Using Cement Kiln Dust as Source ofDivalent Cations and Proton-Removing Agents

Protocol A. Slaking

-   -   1. Cement kiln dust (318.01 g) was weighed into a 500 mL plastic        reaction vessel.    -   2. Deionized water (319.21 g) was added to the reaction vessel        resulting in a 1:1 ratio of cement kiln dust to water.    -   3. Resultant mixture stirred until a homogeneous slurry.    -   4. Reaction vessel closed and sealed with tape.    -   5. Slurry rotated for 18 hours.

B. Precipitation

-   -   1. Deionized water (680 mL) combined with homogeneous slurry of        cement kiln dust in a 2 L plastic reaction vessel with large        stir bar, resulting in a reaction mixture that was about 318 g        cement kiln dust per liter.    -   2. The reaction mixture was stirred at 250 rpm until a stable pH        level was reached (pH 12.41)    -   3. 15% CO2 in compressed air was added (CO2: 0.4 scfh;        compressed air: 2.1 scfh; total: 2.5 scfh) using a sparger        placed as low in the reaction mixture as possible (without        disturbing the stir bar).    -   4. Reaction vessel was covered, leaving only a small opening for        the gas tubing and pH probe.    -   5. Continued to sparge 15% CO2 in compressed air into reaction        mixture overnight.    -   6. CO2 sparging was stopped (by removing the sparger), the        reaction vessel was sealed, and the precipitation reaction        mixture was allowed to stir overnight at 250 rpm.

Work Up 1. pH of the precipitation reaction mixture was measured at pH6.88 after stirring overnight.

-   -   2. Stirring was stopped and the precipitation reaction mixture        was filtered.    -   3. Resultant precipitation material was dried overnight at 50°        C.    -   4. Resultant supernatant was collected.

Analysis 1. Precipitation material was analyzed by SEM, XRD, TGA,coulometry, and percent soluble chloride. FIG. 6 provides an SEM imageof the precipitation material at 2,500× magnification. FIG. 7 providesan XRD of the precipitation material. FIG. 8 provides a TGA of theprecipitation material. Coulometry indicated that the precipitationmaterial was 7.40% carbon. The percent soluble chloride in theprecipitation material was found to be 2.916% soluble chloride.

-   -   2. Supernatant was analyzed using alkalinity and hardness.

TABLE 4 Reaction profile for Example 3. CO2 Delivered CO2 Air Time (min)pH (moles) (on/off) (on/off) 0 12.41 0.000 Off Off 1 12.41 0.008 On On 212.37 0.015 On On 5 12.32 0.038 On On 65 12.32 0.494 On On 137 12.191.041 On On 177 11.30 1.344 On On 247 10.13 1.876 On On 298 9.25 2.264On On 320 8.04 2.431 On On 356 6.93 2.704 On On 404 6.70 3.069 On On 5396.71 4.094 On On 479 6.73 5.689 On On 1311 6.68 9.958 Off Off 2749 6.889.958 Off Off

Example 4 Precipitation Material Using Cement Kiln Dust as Source ofDivalent Cations and Proton-Removing Agents

Protocol 1. Cement kiln dust (80 g) was weighed into a 1.5 L plasticreaction vessel.

-   -   2. Deionized water (1 L) was added to the reaction vessel and        the resultant mixture stirred at 250 rpm (pH 12.45).    -   3. 15% CO2 in compressed air was added (CO2: 0.3 scfh;        compressed air: 2.0 scfh; total: 2.3 scfh) using a sparger        placed at the bottom of the reaction vessel using suction cups.    -   4. Reaction vessel was covered, leaving only a small opening for        the gas and pH probe.    -   5. pH monitored and recorded for about 4 hours.    -   6. After adequate CO2 was added to the precipitation reaction        mixture (i.e., ˜2× equivalents based on CaO/MgO in cement kiln        dust as measured by XRF), CO2 sparging was stopped, the reaction        vessel was sealed, and the precipitation reaction mixture was        allowed to stir overnight at 250 rpm.

Sample Work Up 1. pH of the precipitation reaction mixture was measuredafter stirring overnight.

-   -   2. Stirring was stopped and the precipitation reaction mixture        was filtered.    -   3. Resultant precipitation material was dried overnight at 40°        C.    -   4. Resultant supernatant was collected.

Analysis 1. Precipitation material was analyzed by SEM, FT-IR, andcoulometry. FIG. 9 provides an SEM image of oven-dried precipitationmaterial at 2,500× magnification. FIG. 10 provides an FT-IR of theoven-dried precipitation material. Coulometry indicated that theprecipitation material was 7.75% carbon.

Example 5 Measurement of δ¹³C Value for Precipitation Material andStarting Materials

In this experiment, carbonate-containing precipitation material wasprepared using a mixture of bottled sulfur dioxide (SO2) and bottledcarbon dioxide (CO2) gases and fly ash as a waste source of metaloxides. The procedure was conducted in a closed container.

The starting materials were a mixture of commercially available bottledSO2 and CO2 gas (SO2/CO2 gas or “simulated flue gas”), de-ionized water,and fly ash as the waste source of metal oxides.

A container was filled with de-ionized water. Fly ash was added to thede-ionized water after slaking, providing a pH (alkaline) and divalentcation concentration suitable for precipitation of carbonate-containingprecipitation material without releasing CO2 into the atmosphere.SO2/CO2 gas was sparged at a rate and time suitable to precipitateprecipitation material from the alkaline solution. Sufficient time wasallowed for interaction of the components of the reaction, after whichthe precipitation material was separated from the remaining solution(“precipitation reaction mixture), resulting in wet precipitationmaterial and supernatant.

δ¹³C values for the process starting materials, precipitation material,and supernatant were measured. The analytical system used wasmanufactured by Los Gatos Research and uses direct absorptionspectroscopy to provide δ¹³C and concentration data for dry gasesranging from 2% to 20% CO2. The instrument was calibrated using standard5% CO2 gases with known isotopic composition, and measurements of CO2evolved from samples of travertine and IAEA marble #20 digested in 2Mperchloric acid yielded values that were within acceptable measurementerror of the values found in literature. The CO2 source gas was sampledusing a syringe. The CO2 gas was passed through a gas dryer (Perma PureMD Gas Dryer, Model MD-110-48F-4 made of Nafion® polymer), then into thebench-top commercially available carbon isotope analytical system. Solidsamples were first digested with heated perchloric acid (2M HClO4). CO2gas was evolved from the closed digestion system, and then passed intothe gas dryer. From there, the gas was collected and injected into theanalysis system, resulting in δ¹³C data. Similarly, the supernatant wasdigested to evolve CO2 gas that was then dried and passed to theanalysis instrument resulting in δ¹³C data.

Measurements from the analysis of the SO2/CO2 gas, waste source of metaloxides (i.e., fly ash), carbonate-containing precipitation material, andsupernatant are listed in Table 5. The δ¹³C values for the precipitationmaterial and supernatant are −15.88‰ and −11.70‰, respectively. The δ¹³Cvalues of both products of the reaction reflect the incorporation of theSO2/CO2 gas (δ¹³C=−12.45‰) and the fly ash that included some carbonthat was not fully combusted to a gas (δ¹³C=−17.46‰). Because the flyash, itself a product of fossil fuel combustion, had a more negativeδ¹³C than the CO2 used, the overall δ¹³C value of the precipitationmaterial reflects that by being more negative than that of the CO2itself. This Example illustrates that δ¹³C values may be used to confirmthe primary source of carbon in a carbonate-containing compositionmaterial.

TABLE 5 Values (δ¹³C) for starting materials and products of Example 5.CO2 Base Supernatant Atmosphere Source δ¹³C Solution Precipitatoin δ¹³CValue δ¹³C Value Base Value δ¹³C Value Material δ¹³C (‰) CO2 Source (‰)Source (‰) (‰) Value (‰) −8 SO2/CO2 −12.45 fly ash −17.46 −11.70 −15.88bottled gas mix

Example 6 Cement Production

A. Cement #1

1. Raw Material Precipitation

1000 mL seawater (pH=8.07, T=20.3° C.) obtained from Santa Cruz Harbor.1 M NaOH a drop wise to seawater. Beginning around pH 10, a precipitateformed as evidenced by the cloudy reaction mixture. Despite continuedaddition of NaOH, the pH did not rise above about pH 10.15. When baseaddition was paused, pH dropped to a lower pH value. The solution becameprogressively cloudy with addition of bases, indicating progressiveprecipitation. After about 20 minutes, the pH stopped dropping when baseaddition was paused. The precipitation reaction mixture was subsequentlyfiltered through a Watman 410 1 μm filter, and filtrate is freeze dried.

2. Cement

Freeze-dried powder produced as immediately above was hydrated by dropwise addition of fresh distilled water to form a cement paste, which wasmixed for about 30 seconds in an agate mortar and pestle until thecement paste had a consistency of toothpaste. The pH of the paste wasmeasured using pH paper, and the pH was found to be between pH 11 and pH12. The cement paste was formed into a sphere, left in the mortar, andsealed (with the mortar) in a resealable plastic bag for one day. Afterone day, the cement sphere was hard and shaped like an egg due toslumping while drying.

B. Cement #2

A cement powder consisting of amorphous magnesium calcium carbonate(AMCC), silica fume, vaterite, and brucite (magnesium hydroxide) wasformulated in the following ratio by mass: 3 AMCC: 5 silica fume: 7vaterite: 0.2 brucite.

The AMCC was precipitated from a seawater desalination plant by-productconcentrated to 46,000-ppm salinity at ambient temperature.Precipitation of AMCC was induced by the addition of sodium hydroxide tothe concentrated aqueous by-product, increasing the pH to above 11 untilprecipitation commenced, and adding sodium hydroxide to maintain pH atpH 11. The AMCC precipitate was continuously filtered from the systemand freeze-dried for storage.

Silica fume was obtained from a commercial source.

Vaterite was precipitated from seawater stabilized with 2 μmol/kg LaCl3at a temperature of about 45° C. Seawater processed by the desalinationfacility was already 5-10 degrees warmer than the incoming seawater.Additional heating to 45° C., should it be needed, may be accomplishedby running the seawater through solar panels prior to precipitation ofvaterite.

Brucite was also obtained from a commercial source.

Water was added to the above mixture in a water:cement mass ratio of0.4:1.0 (L/S=0.4) to form a workable paste with an alkaline pH. Thepaste thickens after about one hour and is set into a hardened cement by2 hours. The cement attained greater than 90% of its compressivestrength over the next several weeks.

C. Cement #3

A cement powder consisting of aragonite, amorphous magnesium calciumcarbonate (AMCC), and fly ash, was formulated in the following ratio bymass: 4 Aragonite: 3 AMCC: 3 silica fume: 0.4 Betonies Clay

The aragonite was precipitated from a seawater desalination plantby-product concentrated to 46,000 ppm salinity at 60° C. Seawaterprocessed by the desalination facility was already 5-10 degrees warmerthan incoming seawater. Additional heating to 60° C., should it beneeded, may be accomplished by running the water through solar panelsprior to precipitation of aragonite. Precipitation was induced by theaddition of sodium hydroxide to the water, increasing the pH to above 9until precipitation commenced, and adding sodium hydroxide to maintainpH at pH 9. The aragonite precipitate was continuously filtered from thesystem and freeze-dried for storage.

The AMCC is precipitated from a seawater desalination plant by-productconcentrated to 46,000-ppm salinity at ambient temperature.Precipitation was induced by the addition of sodium hydroxide to thewater, increasing the pH to above 11 until precipitation commenced, andadding sodium hydroxide to maintain pH at pH 11. The AMCC precipitatewas continuously filtered from the system and freeze-dried for storage.

Fly ash was provided from a coal-fired power plant source.

Water was added to the above mixture at a mass ratio of 0.25:1.0water:cement powder (L/S=0.25) to form a workable paste with an alkalinepH. The paste thickened after about one hour and was set into a hardenedcement by about 2 hours. The cement attained greater than about 90% ofits compressive strength over the next several weeks.

Example 7 Compressive Strength of Hydraulic Cement Mortar CubesComprising Precipitation Material

Hydraulic cement mortar cubes were prepared and tested for compressivestrength in accordance with ASTM C109. As indicated in Table 6 below,hydraulic cement mortar cubes were prepared with 100% OPC, 80%OPC4-1+20% fly ash, 80% OPC4-1+20% PPT 1, 80% OPC4-1+20% PPT 2, and 50%OPC+50% PPT 2, wherein PPT 1 and PPT 2 are precipitation materialprepared as in Example 2. Blends of OPC and precipitation material weremixed dry before combining with water (w/c=0.50). 100% OPC was alsocombined with water in a water/cement ratio of 0.50.

TABLE 6 Compressive strength and flow for hydraulic cement mortarscomprising precipitation material. Compression Strength (psi) Time 80%OPC4-1 + 20% Material 50% OPC + (days) 100% OPC Fly Ash PPT 1 PPT 2 50%PPT 2 1 1891 1470.7 N/A N/A N/A 3 2985.5 3128.8 2622.5 2790 1352.7 73959.8 3830.8 3674 3914.3 2458.3 28  5070.8 4752.5 5347.5 4148 4148 56 5056.1 6562.5 6206.3 Flow 96% 99% 74% 86% 92%

As evidenced by the data presented in Table 6, the compressive strengthof hydraulic cement mortar cubes comprising precipitation material aregenerally equal to or better than hydraulic cement mortar cubes of OPCalone.

Example 8 Preparation of Aggregate from Precipitation Material

The steel molds of a Wabash hydraulic press (Model No.: 75-24-2TRM; ca.1974) were cleaned and the platens were preheated such that the platensurfaces (including mold cavity and punch) were at 90° C. for a minimumof 1 hour.

Some of the precipitation material filter cake from Example 1 wasoven-dried in sheet pans at 40° C. for 48 hours and subsequently crushedand ground in a blender such that the ground material passed a No. 8sieve. The ground material was then mixed with water resulting in amixture that was 90-95% solids with the remainder being the added water(5-10%).

A 4″×8″ mold in the Wabash press was filled with the wet mixture ofground precipitation material and a pressure of 64 tons (4000 psi) wasapplied to the precipitation material for about 10 seconds. The pressurewas then released and the mold was reopened. Precipitation material thatstuck to the sides of the mold was scraped and moved toward the centerof the mold. The mold was then closed again and a pressure of 64 tonswas applied for a total of 5 minutes. The pressure was subsequentlyreleased, the mold was reopened, and the pressed precipitation material(now aggregate) was removed from the mold and cooled under ambientconditions. Optionally, the aggregate may be transferred from the moldto a drying rack in a 110° C. oven and dried for 16 hours before coolingunder ambient conditions.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it should be readily apparent to those of ordinary skillin the art in light of the teachings of this invention that certainchanges and modifications may be made thereto without departing from thespirit or scope of the appended claims. Accordingly, the precedingmerely illustrates the principles of the invention. It will beappreciated that those skilled in the art will be able to devise variousarrangements, which, although not explicitly described or shown herein,embody the principles of the invention, and are included within itsspirit and scope. Furthermore, all examples and conditional languagerecited herein are principally intended to aid the reader inunderstanding the principles of the invention and the conceptscontributed by the inventors to furthering the art, and are to beconstrued as being without limitation to such specifically recitedexamples and conditions. Moreover, all statements herein recitingprinciples, aspects, and embodiments of the invention as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents and equivalentsdeveloped in the future, i.e., any elements developed that perform thesame function, regardless of structure. The scope of the invention,therefore, is not intended to be limited to the exemplary embodimentsshown and described herein. It is intended that the following claimsdefine the scope of the invention and that methods and structures withinthe scope of these claims and their equivalents be covered thereby.

1. A method comprising: a) contacting an aqueous solution with a sourceof metal oxides from a first industrial process; b) charging the aqueoussolution with carbon dioxide from a source of carbon dioxide from thesame or a second industrial process, wherein the source of carbondioxide further comprises SO_(x), NO_(x), mercury, or any combinationthereof; and c) subjecting the aqueous solution to precipitationconditions under atmospheric pressure to produce at least onecarbonate-containing precipitation material, wherein the precipitationmaterial comprises calcium carbonate, optionally in combination withmagnesium carbonate, wherein the calcium carbonate comprises aprecipitation material selected from the group consisting of aragonite,vaterite, and mixtures thereof.
 2. The method of claim 1, wherein thesource of metal oxides and the source of carbon dioxide are from thesame industrial process.
 3. The method of claim 1, wherein contactingthe aqueous solution with the source of metal oxides occurs prior tocharging the aqueous solution with the source of carbon dioxide.
 4. Themethod of claim 3, wherein the source of carbon dioxide is flue gas froma coal-fired power plant or kiln exhaust from a cement plant.
 5. Themethod of claim 4, wherein the source of metal oxides is fly ash from acoal-fired power plant or cement kiln dust from a cement plant.
 6. Themethod of claim 3, wherein the source of metal oxides provides divalentcations for producing the precipitation material, and wherein thedivalent cations comprise Ca⁺, optionally in combination with Mg²⁺. 7.The method of claim 3, wherein the source of metal oxides providesproton-removing agents for producing the precipitation material uponhydration of CaO, optionally in combination with MgO, in the aqueoussolution.
 8. The method of claim 7, wherein the source of metal oxidesfurther provides silica, alumina, ferric oxide, or a combinationthereof.
 9. The method of claim 7, wherein electrochemical methodseffecting proton removal also provide for producing precipitationmaterial.
 10. The method of claim 3, further comprising processing theprecipitation material to form a building material selected from thegroup consisting of hydraulic cement, pozzolanic cement, and anaggregate.
 11. The method of claim 1, wherein the precipitation materialfurther comprises calcite.